Pipelines often use horizontal directional drilling (HDD) to cross rivers, roads and other special sections. The external anti-corrosion coating of the pipeline may be damaged during the pipeline pullback process and is difficult to repair. Therefore, it is necessary to put forward higher requirements for anti-corrosion criteria for HDD pipelines. Cathodic protection (CP) can effectively prevent pipeline corrosion and a vital way to ensure CP effectiveness is to test and evaluate pipelines on-off potential on a regular schedule. However, due to limit of specific process and environmental factors, the standard CP test can only be performed on HDD pipelines at both sides and it is impossible to test and assess the CP protection effect of HDD pipelines at various depths. In this paper, a device is designed to evaluate the effectiveness of CP at various depths of HDD pipelines according to its environment condition, and field test was carried out. The test obtained on-off potential data of HDD pipelines at different depths. It provides an effective method for testing and evaluating the CP effectiveness of HDD pipelines.