In this paper,first,the post-fault HVDC ( High-Voltage Direct Current Transmission) reactive power change laws in time domain are analyzed by using the quasi-steady model of HVDC system.Next,the amplitude and time features of reactive power change are explored through simulation.Then,by comparatively analyzing the reactive power change with or without HVDC,the reactive power recovery delaying effect that HVDC reactive power dynamics exert on the induction motor is illustrated,and the mechanism and pathway by which HVDC reactive power dynamics influence the short-term voltage stability are explored.Finally,an index,namely the change rate of critical slip of induction motor,is proposed to evaluate the influence of HVDC reactive power dynamics on the short-term voltage stability,and the effectiveness of the proposed method is verified by an application example on China Southern Power Grid.