Abstract: To extend the combined deterministic and stochastic systems identification and realization（DSR） method to the AC/DC hybrid systems with multiple DC circuits and realize the automatic state space model identification, a system-order determined method based on singular entropy and Tanh-Sigmoid saturation function is proposed, which has strong anti-noise ability and is more suitable for dense modal systems. On the basis of the determined system-order, a test data set of small-range input-parameter is constructed according to the relationship between the past horizon, future horizon, and the order. By comparing the performance indices of the identification model obtained from each parameter, the optimal identification result is selected. The method does not need to give the system input parameters manually. Finally, the effectiveness and the superiority of the proposed method are verified by the cases of the CIGRE Nordic 32-bus system and China Southern Power Grid.