Abstract: With rapid urbanization, the contradiction between traffic and the environmental pollution caused by it is becoming increasingly prominent. To preserve ground buildings, an increasing number of tunnel schemes are adopted. Urban Karst exploration is based on drilling, supplemented by traditional geophysical methods such as high-density electrical method and shallow seismic reflection method, which are inefficient and difficult to implement owing to site conditions. As a geophysical exploration technology developed in recent years, electromagnetic wave technology has the advantages of high resolution and convenient field operation, which can better reveal the development scale and characteristics of underground Karst. Based on traditional data processing, setting the minimum value, choosing the reflection projection result as the initial model, using the low-pass filtering and angle-limiting technology, and adopting the structure program of continuous survey mode to carry out normalized calculation processing can greatly improve the accuracy of electromagnetic wave CT data interpretation. The findings of this study show that the electromagnetic wave detection technology can be applied effectively in Karst exploration, and its detection results have great guiding significance in urban tunnel engineering.