In this paper, MCNP5 Monte Carlo particle transport software package was used to establish the nuclear-mhdr-v1192ir radiation source model, and put in the three-dimensional voxel model which was converted from CT images taken by patients at different bladder filling degrees to simulate the effect of different bladder filling degrees on the brachytherapy of cervical cancer. The prescription dose was 60Gy. The reference points were selected according to the method recommended by ICRU Report No. 38. The single tube applicator was used. The source position was divided into 18 steps, and the distance of each step was 5mm. The results showed that when the absorbed dose of the reference point a was 60 Gy and the bladder filling degree was 54 ml, the absorbed dose of the bladder reference point was 30.21 Gy, the absorbed dose of the rectal reference point was 49.05 Gy, and the absorbed dose of the femoral head reference point was 6.33 Gy (left) and 6.39 Gy (right); When the bladder filling degree was 328 ml, the absorbed dose was 33.59 Gy at the bladder reference point, 50.19 Gy at the rectum reference point, and 6.15 Gy (left) and 6.12 Gy (right) at the femoral head reference point. The absorbed dose of each voxel on the bladder wall was analyzed, and the dose volume histogram of the bladder was obtained. When the bladder filling degree was 54 ml, V10 = 100%, V20 = 39.69%, V30 = 26.20%, V40 = 17.89%, V50 = 14.48%, V60 = 11.69%; When the bladder filling degree was 328 ml: V10 = 86.07%, V20 = 26.53%, V30 = 15.58%, V40 = 9.44%, V50 = 6.01%, V60 = 3.72%. The conclusion is that when the bladder filling degree is 328ml, compared with 54ml, the absorbed dose at the reference point of rectum and femoral head has no significant change. Although the absorbed dose at the reference point of bladder has increased (3.38gy), the irradiated volume of bladder has decreased significantly at all dose points in the dose volume histogram (the irradiated volume has decreased by 13.16% when the dose is 20GY, the absorbed dose at the reference point of rectum and femoral head has increased (3.38gy), The irradiation volume decreased by 8.45% when the dose was 40 Gy, and 7.97% when the dose was 60 Gy). The simulation results have certain guiding significance for the clinical radiotherapy of cervical cancer.