With the integration of a high share of renewable energy, the spatially uneven distribution of inertia in power systems has become increasingly prominent. Conventional system-level equivalent inertia cannot accurately characterize the differences in the rates of change of frequency and voltage among different nodes after disturbances or the inertia support margins of local nodes. To address this issue, an equivalent complex inertia modeling and margin assessment method for network nodes is proposed. Based on complex-frequency theory, a nodal equivalent complex inertia model is established, and calculation expressions for nodal frequency equivalent inertia and nodal voltage equivalent inertia are formulated. By introducing observation weights and disturbance weights, a node-to-region aggregation model is constructed, and the generalized inertia zone and nodal inertia margin index are proposed to realize inertia adequacy assessment in both frequency and voltage dimensions. Case studies on the IEEE 39-bus system show that the proposed method can characterize the spatial distribution differences of nodal complex inertia and visually identify local areas with weak inertia support through the generalized inertia zone.