The electrical conductivity of soil is controlled by the moisture content. With the voltage on both ends of the protective resistor in the circuit board as the signal to reflect the changes of moisture content, we designed a sensor for the moisture content. The sensors were calibrated in sand and sandy soil to obtain the linear variation relation between moisture content and voltage. The device is applied to the model of landslide induced by fog and rain infiltration to test the changes of moisture content. Results show that through this device we can get the moisture content variation conveniently, quickly and more accurately. It can meet the requirements of the landslide model test, but the infiltration relation and the influence of temperature were not taken into consideration. Further research and improvements are needed.