The power system under new energy penetration has a low level of inertia and high uncertainty, and the frequency response process between the nodes in the system is spatio-temporally correlated, and quantifying the spatio-temporal correlation of the frequencies between the nodes is a technical means of estimating the inertia of a new type of power system. Firstly, the frequency spatio-temporal dynamic process of the power system under active perturbation is analyzed; secondly, the index of node computational inertia is defined; then, the power oscillation characteristics among units after active perturbation are analyzed and the oscillating power micro-increment is computed, and then the expression of node computational inertia is deduced; lastly, the simulation is verified by using the IEEE39 node system, and the resulting error of node computational inertia is within 7%, and the average error is 2.93%. The results indicate that the proposed method for calculating node inertia can accurately determine the magnitude of node inertia, demonstrating practical utility.