A spectrum observation device has been designed for measuring the electrical spectrum parameters of outdoor geological outcrops. The signal sending end adopts multi stage current expansion output or voltage power amplification output to increase the load capacity of the sending signal; On the basis of common clock synchronization, the receiver and transmitter improve the anti-interference ability of the device through coherent detection, and use weak signal detection technology to design preamplifiers, signal conditioning and other circuits to improve the signal-to-noise ratio of the channel. By calibrating the observation device using a standard resistance capacitance network model and conducting on-site experiments, spectral observation of underground conductive media was achieved. The results show that the device has signal transmission mode and multi gear switching function, automatic frequency conversion measurement, simple operation, and the observation results play a certain supporting role in selecting exploration methods, establishing geophysical models, and geological interpretation.