Large － scale access of distributed generation to urban power grid will have certain impact on the fault characteristics of urban power grid，and the randomness of its output will cause uncertainty of the fault characteristics． Aiming at the fact that the existing random analysis methods do not consider the influence of output randomness，a failure analysis method for urban power grid with distributed generation based on Monte Carlo method is proposed． Based on the probabilistic model of distributed generation output，Monte Carlo method is used for random sampling，and then the fault model under PQ control and low － voltage ride － through strategy is used to calculate the probability distribution of fault voltage and short － circuit current． Finally，it is verified with a calculation example． The results show that the fault characteristics of distributed generation connected to urban power grid have probabilistic characteristics． The proposed method can obtain the probability distribution of fault voltage and short － circuit current，and can provide a basis for the analysis of fault characteristics of urban power grid and the selection of setting values