Objective: To investigate the clinical effects of pedicle screw internal fixation combined with posterior lumbar interbody fusion in treatment of lumber instability. Methods: 60 cases lumbar instability patients were equally and randomly divided into control group and observation group. The patients in control group were only treated with pedicle screw internal fixation, and patients in observation group were treated with pedicle screw internal fixation combined with posterior lumbar interbody fusion. The total effective rate, pain relief time and hospital stays of 2 groups were compared. Results: The pain relief time and hospital stays of patients in observation were obviously shorter than control group, but total effective rate was obviously higher (P<0.05). Conclusions: Pedicle screw internal fixation combined with posterior lumbar interbody fusion has remarkable clinical effects on treating lumbar instability, it can shorten pain time and hospital stays effectively, so it is worthy of spreading.