Convicted killer Kai Yuen, 34, appeared in the ACT Supreme Court for a sentence hearing for recklessly inflicting grievous bodily harm on a fellow inmate.

Yuen, appearing in court in a dark grey suit flanked by corrections officers, had earlier pleaded guilty to the attack which took place in November last year.

The court was shown graphic footage in which Yuen and the other detainee can be seen throwing punches at each other before the other detainee is seen wiping blood from his face and leg.

The footage began with both men entering Yuen's cell before they both exit and pace around a common downstairs area appearing to talk to each other.

Documents tendered in court said Yuen could be seen with his hand in his right pocket where it is suspected he later pulled the weapon used to violently slash the other detainee.

The men enter Yuen's cell again and within seconds a brawl begins with punches thrown. The detainee then grabs Yuen around the chest and drags him out from the cell and onto the 'catwalk', the raised walkway outside the cells.

The detainee moves away from Yuen and appears to grab his leg before Yuen continues to advance at him.

The men trade more punches and at this time Yuen appears to be holding something in his right hand which makes contact with the other detainee's face on multiple occasions.

The fight continues along the catwalk and the detainee can be seen wiping his face, which is covered in blood.

Corrections officers proceed to get other inmates into their cells and then convince the two men to separate.

The court documents state the detainee required immediate first aid and the jail doctor was called before the detainee was transferred to the Canberra Hospital.

He suffered lacerations to his face, chest, abdominal area, hip, knee and arms, some of which required plastic surgery.

Defence barrister Theresa Warwick told the court both Yuen and the other detainee acted as aggressors in the altercation.

She suggested Yuen's actions could be seen as self defence but conceded that as self defence his actions were excessive.

She also tendered a number of certificates of courses completed by Yuen to the court, including a hairdressing course and anger management courses.

Documents state Yuen was later questioned about the whereabouts of the weapon to which he said "I got rid of it". It's believed he flushed it down the toilet.

Yuen is currently serving 28 years for the murder of his former friend Brendan Scott Welsh and an earlier jail bashing.

He is eligible for parole in 2030.

He is due back in court in February next year.