Soil water flux measurement is very important in agriculture, but there is currently no mature measurement equipment. Through technical analysis, a soil water flux sensor was designed using Pyboard control unit, MicroPython programming language and ADS1256 analogtodigital conversion chip. By using Python software and Matplotlib functions in the Math library, the host computer software was designed. Through sensor function tests, soil thermal diffusion coefficient, volumetric heat capacity, thermal conductivity, and soil water flow measurement can be achieved. Four kinds of soil samples were selected for testing, and the calculated values were obtained according to the maximum dimensionless temperature difference (MDTD) method and the ratio (Td/Tu) method, which were compared with the actual water flow. The test results showed that the system had high measurement accuracy and stable operation. In the application of the method, the linearity between the calculation results of the two algorithms and the actual values was good. The determination coefficient R2 of the MDTD method of the four soils were 0.9677, 0.9798, 0.9780 and 0.9647, and the determination coefficient R2 of the Td/Tu method were 0.9845, 0.9985, 0.9989 and 0.9986, indicating that the system had good measurement accuracy. Through adaptability evaluation, the correlation between the calculated values of Td/Tu and actual values in the four soils was better, the error was lower, and the calculation results were better than the MDTD method, which provided guidance for the selection of system algorithms. 