The nested fast and simultaneous solution (NFSS) algorithm can significantly improve the simulation speed by node-elimination in the circuit. However, the equivalent circuit of a permanent magnet synchronous generator (PMSG) model provided by commercial simulation software cannot be obtained. This limits the application of the NFSS algorithm in the simulation of an offshore wind farm (OWF). To fill this gap, this paper aims to provide an electromagnetic transient (EMT) equivalent modelling method of PMSG and analyze the stability of the modelling method. First, a mathematical model of the PMSG is discretized and thus the equivalent circuit represented by a three-phase controlled current source is obtained. Then the interface method, control mode, and equivalent solution procedure of PMSG is given. The stability of the equivalent modeling method is analyzed considering the actual PMSG parameter. Finally, a detailed model (DM) and equivalent model (EM) are built in PSCAD/EMTDC to verify accuracy and stability. The results show that the proposed model has good accuracy and that the stability analysis is correct. This provides a model basis for the application of the NFSS algorithm in OWF and constraint conditions for the parameter selection of a generator.