With the continuous increasing proportion of the converters, the moment of inertia and damping of power systems are reduced, which has a non-negligible impact on the safe and stable operation of the new power system. At present, the Nyquist criterion and the generalized Nyquist criterion are often used to judge the stability of the grid-connected converter system. However, both are based on the premise that no right-half-plane (RHP) pole exists in the impedance ratio. To solve this problem, on the basis of establishing single-input single-output (SISO) impedance model considering coupling between positive and negative sequence, as well as coupling between source and load, a stability analysis method considering the RHP pole is proposed. First, the number of RHP poles and the number of Nyquist curve bounding points (−1, j0) of the research system are estimated. Secondly, combining with the Nyquist criterion, the stability of systems with RHP poles can be accurately judged by using an impedance Bode diagram of the SISO system. Finally, based on the electromagnetic transient simulation model built in Matlab/Simulink, it is verified that the proposed method can effectively analyze the small-signal stability of the system with or without RHP poles.