Abstract: The low system inertia caused by high renewable energy penetration has affected system frequency stability with large disturbances, and the frequency indicators are getting closer to the safety boundary. In order to quantify system frequency response capability and clarify operating boundary, this paper described the necessity of system inertia requirement and proposed a system minimum inertia estimation method considering the rate of change of frequency (RoCoF) and frequency nadir. In terms of RoCoF constraints, static load voltage characteristic was introduced into the estimation model, and the frequency relationship between the center of inertia and the disturbance bus was quantified according to the power distribution mechanism; In terms of frequency nadir constraint, the minimum inertia was estimated by establishing a frequency response model with multiple types of resources. The characteristics of the minimum inertia requirement of the system under both constraints were analyzed. According to the lack of inertia under different frequency constraints, the mitigation measures were given, and the relationship between each measure variable and the minimum inertia was analyzed. Finally, the WSCC 9 bus system and large system were used to verify the effectiveness and accuracy of proposed method, which provides theoretical basis for the stable operation of the system.