To efficiently achieve in-depth detection of the deposit-bedrock interface of potentially unstable slopes, a ground-penetrating radar for the unmanned aerial vehicle was developed. The principle of the stepped-frequency continuous wave ground-penetrating radar prototype system was analyzed, and this study demonstrated the key parameters of the unmanned aerial vehicle-borne ground-penetrating radar prototype system. Based on the measurement principle, scanning frequency mode, and the feature of being able to perform time-domain reflectometry measurement of the vector network analyzer, this study selected the lightweight N9914A handheld vector network analyzer to develop a radar transceiver. Specifically, the handheld terminal is used as the master computer, the acquisition software is deployed and the written script file is imported. And vector network analyzer is controlled through the network interface to automatically store data files by time. A small-sized (66 cm×10 cm×0.1 cm) low-frequency air-coupled antenna was developed to achieve the radiation and reception of the stepped-frequency continuous radar waves, and a prototype system of low-frequency unmanned aerial vehicle-borne ground-penetrating radar based on a handheld vector network analyzer was integrated. Through performance and transceiver function tests of the prototype system, the results show that the working bandwidth of the system reaches 20 to 150 MHz and the signal transmission power is greater than 5 W, and its transceiver function meets the requirements of the experimental design. The prototype system was mounted on an unmanned aerial vehicle, and field tests were conducted at the Dayangping landslide site in Xiaoshui Town, Yingshan County, Sichuan Province. The results show that the depth of the reflection interface in the 7.7′Bscan image of the survey line is approximately 11.5 m (the relative dielectric constant of the soil is 9), which is consistent with the stratified interface of silty clay and mudstone in the known geological section, meeting the requirement of a detection depth greater than 10 m.