Objective To detect the factors that affect the prognosis of expansive open-door laminoplasty. Methods 30 patients who underwent expansive open-door laminoplasty were selected and were followed upfor more than 24 months. The preoperative JOA scores and the last follow-up JOA scores were obtained. The increase in sagittal canal diameter(SCD),the laminoplasty opening size(LOS), the laminoplasty opening angle(LOA), and C3～C7 lordosis angle(LA)were measured by the imaging data in perioperative period. With consideration of age, sex, operation time and bleeding during the operation, the association among the above mentioned parameters were analyzed. We also analyzed the relationship between those parameters and improvement rate of nerve function postoperatively. Result The preoperative average JOA scores was(10.13±2.16)and the postoperative average JOA scores was(13.97±1.78)at the last follow-up. The average improvement rate of nerve function was(56.22±22.47)%. The analysis showed that when the age was 70 or older, the improvement rate of JOA scores significantly decreased, and the difference in age was statistically significant(P＜0.05). There was no significant difference in improvement between different gender groups(P＞0.05); The preoperative JOA scores and the postoperative JOA scores were related positively significantly(P＜0.01). The age was not related with the preoperative JOA scores, but it was related negatively significantly with the postoperative JOA scores(P＜0.05). The SCD, LOS and LOA were related with each other significantly(P＜0.01). The LA was not related with the SCD, LOS or LOA; The improvement rate of nerve function and the LOS were related significantly(P＜0.01). The improvement rate of nerve function also was related to the SCD(P＜0.05). Conclusion The SCD, LOS and LOA are related significantly. The LOS and SCD are related significantly with the improvement rate of nerve function after ELAP.