Landslides have been occurring frequently because of rainfall, which leads to serious consequences, often plugging rivers, disrupting transportation, communication, and other lifeline projects and posing a serious threat to people's life and property. Therefore, effective early warning system for rainfall-induced landslide is particularly important. This research presented the development of early warning system that includes soil moisture sensor, temperature sensor, and data transmission system. Some tests were carried out to evaluate the feasibility of the developed system under different water contents. Test with different sample depths under the same water content was also used to verify the accuracy of this system. The results show that, the sensitivity of the sensor is affected by the initial state, and it takes about 10–20 min to reach the stable measurement state. With the increase of water content in soil samples, the resistance value obtained by the system decreases accordingly, which is consistent with theoretical results. The tests of early warning system also worked well under different depths of the same soil sample. The development of the current warning system is the basis for predicting landslides in the future, and lower development costs and accurate test results make it possible to be widely adopted to both the developed and developing nations.