Inspectors at HMP Channings Wood near Newton Abbot say there's been no changes since the last inspection in 2016.
It's been deemed as "not sufficiently good" which is the second lowest assessment.
Levels of violence were found to be rising among the 724 men housed there, with nearly two thirds of inmates claiming to have felt unsafe.
Following the inspection the probation service say 22 extra officers have been recruited to provide key workers for every prisoner - and they have 'increased resources to improve safety and accommodation conditions'.
Peter Clarke, HM Chief Inspector of Prisons, said the training and resettlement prison environment 'reflected stark contrasts'.
He said: "Much of the accommodation was of a good standard and prisoners appreciated their access to the pleasant surrounding grounds.
"On three units, however, in our view, failures of leadership had led to some very poor standards with prisoners living in often bleak and dirty cells.
"There had been efforts to improve safety at the prison, which held up to 724 men, but these were often uncoordinated, which undermined their effectiveness.
"Nearly two-thirds of prisoners had felt unsafe in the prison at some point, with a third still feeling unsafe at the time of the inspection.
"Violence was rising but inspectors were concerned about the prison’s efforts to tackle it.
"The report noted 'levels of violence had increased and were high. Although reported data were comparable to other category C prisons, we also found evidence of significant under-reporting that managers were aware of but had not yet addressed'.
"We were not assured that that the well-being of vulnerable prisoners was always sufficiently safeguarded and the prison lacked a coordinated approach to the reduction of violence linked to the problem of drugs.
"Over three-quarters of prisoners thought illicit drugs were easy to access.
"Inadequate supervision of prisoners, for example, meant there were repeated opportunities for drug misuse and associated violence.
"Since the last inspection two prisoners had taken their own lives and the number of self-harm incidents had doubled.
"Work to promote equality had deteriorated since 2016, though, more positively, most prisoners felt respected by staff and indicated that they knew who to turn to for help.
"Here, again, however, inspectors observed variability and polarisation.
"We saw much positive work being undertaken by staff of all disciplines working appropriately to set and maintain standards.
"On the poorer wings, in contrast, we found staff congregating in offices, failing to set standards or maintain supportive living conditions and failing to challenge delinquent behaviour on the part of prisoners.
"Inspectors noted that the significant number of newer, less experienced officers needed greater support.
"However, more positively, prisoners had reasonable access to time out of cell.
"The prison had sufficient full-time activity places for most men but the management of attendance and punctuality was poor and quality of teaching, learning and assessment required improvement.
"Public protection measures, as well as release and resettlement planning, were weak and inconsistent."
Overall, Mr Clarke said: "Inconsistency of outcomes was a recurrent theme of our findings at this inspection.
"This was best exemplified in varying standards being accepted across the different accommodation wings, but also in the way initiatives to bring about improvement were often implemented in a partial or uncoordinated way.
"Managers were enthusiastic and open about making progress, but optimism and energy needed to be harnessed in a way that ensured leaders at all levels were visible, demanding consistent standards, and ensuring improvement was embedded and sustainable."
Michael Spurr, Chief Executive of Her Majesty's Prison & Probation Service, said: "We recognise the need to achieve greater consistency in order to improve standards across the prison, which is the Governor’s priority.
"But I am pleased that the Inspectorate acknowledge a range of positive work being undertaken by staff at all levels at Channings Wood.
"An additional 22 officers have now been recruited to provide key workers for every prisoner, and we have increased resources to improve safety and accommodation conditions."
The full report can be found here