The objective of this study was to select factors related to the prognosis and curative effect for posterolateral fusion (PLF) of lumbar low-grade isthmic spondylolisthesis (LGIS). Of 125 patients who accepted PLF treatment, 119 obtained solid union in this prospective study. Statistical analysis was used to evaluate factors related to the prognosis and curative effect. Spondylolisthetic position (L4, L5), gender and postoperative percent disc height were not significant factors for the prognosis and curative effect. Length of disease history (LDH), preoperative Japanese Orthopaedic Association (JOA) score and postoperative percentage of slipping (% slip) were significantly related to postoperative JOA score and postoperative improved JOA score. LDH and postoperative % slip were significantly related to postoperative recovery rate. LDH, preoperative JOA score and postoperative % slip were independent related factors for the prognosis and improvement of LGIS. LDH and postoperative % slip were independent related factors for the curative effect. However, age, gender, spondylolisthetic position and postoperative percent disc height were not significant factors.