The invention belongs to the technical field of new energy bearing capacity analysis, and particularly relates to a new energy bearing capacity early-warning method based on the online inertia estimation of a power system. The method comprises the following steps: 1, analyzing a system frequency response characteristic curve, and determining key parameters for determining the system frequency change; 2, obtaining the ultimate moment of inertia of the system under the maximum disturbance through simulation according to the constraint condition of system frequency change; 3, evaluating the new energy bearing capacity by comparing the rotational inertia obtained by the online estimation of the system with the ultimate rotational inertia. According to the invention, the method can give the newenergy bearing capacity of the system in real time according to the operation condition of the system, which is of important significance to ensure effective utilization of new energy and safe and stable operation of the system. Under the condition that the new energy permeability in the power system is large, when the power of the system is unbalanced, the frequency instability of the system canbe judged in time by analyzing the frequency change rate and the frequency offset, and early warning is given out.