Abstract: The new version of the "Code on security and stability for power system" states that the short circuit ratio (SCR) of renewable energy plants should reach a reasonable level. However, specific evaluation standards are insufficient, and it is impossible to quantify the stability of the power-electronic interfaced generators. To fill the gap, a unification stability criterion for the power system integrated with power-electronic interfaced plant was proposed in this paper. First of all, the definition and characteristic on unification stability index of dynamic state (USI₁) were expressed, and the stability risk on the scale of electromagnetic simulation was measured, which based on robust control theory and multivariable frequency domain control theory. Secondly, ignoring the dynamic characteristics of renewable energy sources, power system and their control system, USI₁ could be degenerated into unification stability index of static state (USI₂) on the scale of electromechanical simulation to realize efficient risk scanning. Then, a dynamic two-dimensional index framework was constructed to improve the efficiency and accuracy of plant stability assessment. Finally, the case, which based on the power electronics dominated power system in the Northwest of China verified the effectiveness of the proposed method.