In this study, Monte Carlo method is applied to evaluate dose distribution in radiotherapy.This method has following advantages:1.Overcoming some defects in other methods, the method can guarantee the accuracy.2.Considering the real composition of tissue and the geometric shape of the organ, the calculation has higher accuracy.3.The method is easy to use and popularize in clinic.By use of this method the internal and external radiation dose can be coordinaed each other more accurately and better, so that the 5 years survival rate may be increased.The treatment result is improved.The principle of the new method can be popularized to other hospitals or radiation centers for routin radiotherapy and after-loading system in carcinoma of uterine cervix.