Objective To investigate the accuracy of preoperative three-dimensional reconstruction of tumor in craniotomy for supratentorial convex brain tumors, and to provide an accurate and safe auxiliary method for craniotomy. Methods Patients with supratentorial convexity brain tumors who were admitted to the Department of Neurosurgery, West China Hospital, Yibin Hospital, Sichuan University between April 2018 and November 2020 were prospectively enrolled and randomly divided into reconstruction group and control group. In the reconstruction group, preoperative three-dimensional reconstruction of the tumor was used for craniotomy positioning, while in the control group, traditional two-dimensional tomographic imaging was used. The basic conditions, intraoperative localization and tumor exposure satisfaction rate, maximum diameter of bone window, operation time, cerebral draining vein injury, and postoperative subcutaneous effusion or intracranial infection were compared between the two groups. Results A total of 43 patients were included, 22 in the reconstruction group and 21 in the control group. There was no significant differences in age, gender composition, incidence of midline shift, tumor growth site and tumor size between the two groups (P>0.05). There was no significant difference in the incidence of cerebral drainage vein injury and postoperative subcutaneous effusion or intracranial infection between the two groups (P>0.05). The satisfaction rate of intraoperative positioning and tumor exposure in the reconstruction group (95.5% vs. 66.7%) was higher than that in the control group, the maximum diameter of the bone window [(6.26±1.32) vs. (7.31±1.13) cm] and the operation time [(194.00±22.76) vs. (214.57±26.53) min] were lower than the control group, and the differences were statistically significant (P<0.05). Conclusions Preoperative three-dimensional reconstruction helps to locate the tumor more accurately, improves the satisfaction rate of tumor exposure, reduces the diameter of the craniotomy window, and shortens the operation time. Compared with traditional two-dimensional tomographic positioning, it has more advantages.