Transport officers were dealing with an unrelated matter on a platform when Mark Thompson allegedly approached Constable Hayden Edwards and stabbed him from behind about 6.45pm on Good Friday.

The 30-year-old officer was taken to Royal Prince Alfred Hospital where he underwent surgery for a 6cm cut to his back overnight.

Const Edwards was discharged from the hospital on Saturday evening.

It is alleged Thompson used a 45cm hunting knife with a 30cm blade, Assistant Commissioner Karen Webb said.

"Having seen an image of that knife - our officer is very lucky to only have minor injuries," Ms Webb told reporters on Saturday.

"(It) was an unprovoked attack. We allege the offender has approached with some vigour."

Thompson was arrested after being stunned with a Taser and taken to St Vincent's Hospital where he was treated for a cut to his head.

The 53-year-old was released from hospital on Saturday morning and taken to Sydney Police Station.

He was charged with wounding with intent to cause grievous bodily harm, using an offensive weapon to prevent lawful arrest, resisting arrest and having a knife in a public place.

Thompson did not appear in court when his matter was heard at Parramatta Bail Court on Sunday morning.

Bail was not applied for and it was formally refused.

Const Edwards, who has been a member of the police force for three years, moved to Sydney only recently after transferring from Moree in northern NSW.

Chief Inspector Paul Carrett said the "very competent" officer was sore and tired after the attack.

"A stabbing of a police officer - unprovoked - is a very serious matter," Insp Carrett.

The police union described the attack as "cowardly" and said it highlighted the dangers police officers face on the job.

"The offender has just walked up behind the police officer, who was doing his job talking to someone else, and stabbed him in the back," Police Association of NSW president Tony King told reporters on Saturday.

"It's a cowardly act from behind."

Thompson's matter will next appear before Central Local Court on June 18.

Australian Associated Press