OBJECTIVE To study middle period curative effect of posterior lumbar intervertebral fusion (PLIF) and interspinous dynamic fixation (Wallis) in the treatment of L45 degenerative disease and its influence on adjacent segment degeneration. PATIENTS AND METHODS 66 patients with lumbar L45 degenerative diseases were selected for study. The patients were randomly divided into PLIF operation group and Wallis operation group with 33 cases in each group. The patients were analyzed for T1ρ value, functional score and UCLA classification of L3/4 and L5/S1 segment in different periods of two groups of patients. RESULTS The level of T1ρ for L3/4 and L5/S1 segment in two groups between preoperative period and last follow-up showed a decreasing trend, while level of T1ρ value of L3/4 segment in PLIF operation group was significantly lower than Wallis group. Within group comparison, the level of T1ρ for L3/4 segment in PLIF operation group until the last follow-up was significantly lower than that before operation. While comparing two groups, ODI scores after operation for PLIF group and Wallis group was significantly lower than those before operation and JOA score was significantly higher than that before operation. The UCLA grade of L3/4 and L5/S1 segment of the two groups was significantly improved compared with that at the time of the last follow-up. CONCLUSIONS Both PLIF and Wallis methods are effective for the treatment of lumbar degenerative disease of L45. Wallis operation has slight advantage in slowing down the speed of intervertebral disc degeneration in the upper adjacent segment of the patient.