Abstract: Model analysis based frequency response analysis after the power disturbance is important for the security assessment and emergency control of power systems. When the power grid fault occurs, the magnitude drop of the grid-connected voltage of direct-drive wind turbine（DDWT） causes the transient response of the controller. Meanwhile, the sudden change in the voltage phase triggers the transient response of the phase-locked loop（PLL）, which generates the power control error through the converter control conduction. And the power control error may lead to a large deviation in the existing frequency characteristic analysis targeting the sudden load change scenarios. Therefore, a quantification method for the phase-locked deviation of DDWT under the power grid fault is proposed. The conduction paths of phase-locked deviation through converter control of DDWT are analyzed. Also, the mechanism and calculation method for the power control error of DDWT caused by the transient response of the PLL are proposed. The frequency response model of the power system with DDWT under the power grid fault is established, and the calculation method for the rate of change of frequency and the maximum frequency deviation under the influence of the transient response of the PLL is proposed. The frequency dynamic response characteristics of the power system considering the power control error of DDWT under the power grid fault are analyzed. Finally, the effectiveness of the proposed method is verified through case studies.