The victim, 40, was stabbed in his lower abdomen in Brintons Park, Sutton Road, at around 22:00 GMT on Friday.
He was taken to hospital, where his condition is described as stable, West Mercia Police said.
Det Sgt Jason Maiden said: "This was a nasty attack that has left a man with serious injuries and it could have been a lot worse.
"We are still trying to piece together exactly what happened and at this time we are appealing for anyone who was in the area at the time and who may have seen the incident or something suspicious to contact us."
Police are appealing for witnesses after a man was seriously injured in a stabbing in a Kidderminster park.