Commercial sensors of soil moisture normally cannot specifically observe the customized water content of soil profile, with emphasis on unadjustable measurement depth, interchange errors among multi-sensor probes, high cost, and difficulty in power supply for long-term monitoring in the field. In this study, a novel solar-powered system was developed to in-situ and long-term monitor the water content of soil profile in the field using dielectric tube sensors. Three parts included the power supply, measurement, and storage subsystem. The power supply subsystem was composed of the solar and lithium battery for long-term monitoring of the water content of soil profile in the field. A control panel was also utilized in a measurement subsystem to control the vertical movement of a dielectric tube sensor and simultaneously measure the soil water content and depths of the soil profile. The communicated system was installed with the upper computer software through Bluetooth. The operational parameters were set flexibly in the actual requirements, including the depths, spacing distance, and measuring periods. A storage subsystem was then used to record real-time measurements of the water content of the soil profile. A series of experiments were conducted to validate the performance of the developed system. The maximum output power of the solar panel was 5 W, greater than the working power (1.4 W) and the standby power of the system (0.35 W), which can make it possible for the system to achieve long-term endurance in the sunny outdoor. The solar-powered supply test showed that the novel system satisfied the high requirements of long-term running with the combination of solar and lithium batteries. The system lasted about 13 d without light, whereas worked sustainably under sufficient light. In addition, the voltage of the lithium battery changed by 3.2 V during the whole discharge, while the output voltage of the sensor only changed by 5 mV, indicating that the output voltage of the sensor was fully independent of the voltage of the lithium battery. A drip irrigation experiment was performed on two soil samples (sand and silt loam soil) with different drip irrigation rates, further to test the position accuracy of a system. High accuracy was achieved in the measurements of soil water content with a high consistent relationship (R2 >0.99) between actual volumetric water contents and converted one via the calibration curves of the sensors. The novel system accurately positioned the depth of the sensor probe in the soil profile with a positioning error of less than 0.2 cm. Furthermore, the infiltration experiments in two drip irrigation showed that the developed system accurately and completely characterized the dynamic of water content in soil profiles during infiltration with different drip irrigation rates. The finding can provide reliable technical support to in-situ monitoring the crop growth state and moisture change of root zone for reasonable irrigation strategy.