Equivalent modeling for the wind turbine generator system（WTGS） is the foundation for studying wind farm grid integration. A new equivalent method is proposed based on auto mutation particle swarm optimization（AMPSO） algorithm for doubly-fed WTGS. Taking wind turbine patterns as the grouping rule for WTGS， the doubly-fed WTGS equivalent model is obtained by simplifying the control strategy. According to the effect of parameters on the operational characteristics of doubly-fed WTGS， the parameters are divided into transient and steady-state parameters， and calculated by test measurement method and AMPSO algorithm respectively. Simulation results demonstrate that the equivalent model is accurate and simple， and is applicable to the analysis and calculation for the large-scale wind farm integration.