The large scale wind turbine integrated into grid has changed the transient characteristics of the traditional power system dominated by synchronous generators. In addition, the random fluctuation of wind power output will affect the transient stability of the power system. Therefore, a power system time domain simulation method based on affine arithmetic is proposed to consider the fluctuation of wind power output. Based on the transient model of doubly fed wind turbine (DFIG), the electromechanical transient model of power system is firstly extended, and the electromechanical transient affine model of power system considering the input power fluctuation of DFIG is established. The affine model is transformed into an iterative Jacobian affine matrix equation by implicit trapezoidal integral method. Simulation results show that the proposed affine method can obtain the interval boundary of power system transient response faster than Monte Carlo simulation without assuming the probability distribution of input uncertainty.