The invention discloses a method for improving the expansibility of a deep neural network power flow model, which mainly comprises the following steps: (1) acquiring basic data of a power system; (2)determining a feature vector; (3) establishing an original DNN power flow model; (4) training the original DNN power flow model to obtain a trained original DNN power flow model; (5) expanding the original DNN power flow model to obtain an expanded DNN power flow model; and (6) calculating the probabilistic power flow of the expanded system to obtain a probabilistic power flow result. The method can be widely applied to the calculation of the probabilistic power flow of the power system, and is particularly suitable for the situation in which the DNN of the original system is not suitable forbeing used due to the expansion of the system.