Dean Simpson of Manor Drive, Halton Holegate, Spilsby pleaded guilty when he appeared at Lincoln Crown Court on Thursday June 23.
The court heard emergency services attended Manor Drive at Halton Holegate on Sunday January 9 after reports of an altercation.
The woman victim sustained serious but not life-threatening injuries consistent with a knife wound and was taken to hospital.
Simpson will reappear at Crown Court on August 12 for sentencing.