An appropriate transient model of wind farm is demanded for researches about the impacts of large scale wind generation. Firstly, the influence factors which should be taken into consideration of the transient model selecting for wind farm are investigated in view of four aspects as follows, the installed capacity of wind farm, types of wind farm, the point of interconnection of wind farm and the arrangement of wind turbines. Secondly, the calculation method of threshold selection for different transient models of wind farms for system simulation which meets the requirement of the error evaluation index is proposed and a practical criteria for selecting the transient model of wind farm is presented. Finally, the effectiveness of the proposed method is verified based on an actual regional power grid.