The purpose of this study was to investigate the factors of fracture type progression during conservative treatment of fragility fracture of pelvis (Rommens classification type II). 71 patients with Rommens classification type II (a, b, c) who underwent conservative treatment and had multiple CT scans were selected from 177 patients treated in our department over 8 years from 2011. The results were as follows. In this study, we compared the factors of fracture type progression in 25 patients in the progression group and 46 patients in the non-progression group. In the group of patients who progressed to Rommens classification type II to IIIc, there were more fractures of the suprapubic branch and both pubic symphysis, and in the group of patients who progressed to Rommens classification type II to IVb, there were more cases without a clear history of falls, and the anatomical Pelvic Tilt and Pelvic Incidence were higher.