As renewable energy and power electronics continue to grow in proportion, the power system is increasingly exhibiting traits of lower inertia and spatial-temporal dispersion. It deteriorates the frequency response and system stability. The majority of existing studies focuses on the estimation of system inertia, while there is a lack of in-depth studies on the characteristics and properties of the inertial spatial-temporal distribution. This paper evaluates the nodal inertia of the power system by examining its spatial and temporal distribution characteristics. A model for nodal inertia representation is developed based on the correlation between frequency and power, allowing for an estimation of inertia. Spatial distribution index and time-varying index are introduced to analyze the changing process of inertia distribution under disturbances in both dimension for further assessment. Finally, using the IEEE 3-machine 9-bus system, the system nodal inertia is assessed, the characteristic of nodal inertia is discussed and analyzed deeply.