The invention discloses a three-dimensional digitalized monitoring device for a substation grounding grid and an evaluation method. The three-dimensional digitalized monitoring device comprises a microcontroller, an adjustable direct-current constant current source, a current channel changeover switch module, a multi-channel wiring socket, a voltage channel changeover switch module, a signal processing module, a data storage module, a wireless communication module and an upper computer. The microcontroller is used for controlling output current, an analog voltage signal is output through a D/A (digital/analog) module and enters the adjustable direct-current constant current source, and the obtained voltage signal is used for storing data in a SD (secure digital) card through a file system by utilizing the current channel changeover switch module, the multi-channel wiring socket and the voltage channel changeover switch module; the acquired data is sent to the upper computer through a wireless device SX1212, and the upper computer is used for calculating branch impedance according to the acquired data through software and performing three-dimensional imaging on a conductor of the grounding grid and surrounding soil.