A kind of portable soil EC sensor was developed. The performance test of the sensor showed satisfactory result. Voltage drop of the sensor had the same trend as soil EC when four electrodes were set in Wenner structure and Schlumberger structure. The highest precision was obtained under the condition of Schlumberger structure (a=15, b=30). Non-linear modeling was also carried out. The 3 models used were power function, polynomial and index function. The best estimation was obtained in power function model. The determination coefficient reached 0.994. The constant of the model coefficients was depended on the sensor structure while the power of the model coefficients did not show that characteristic. It was shown that soil texture and soil density could have an effect on the power of the model coefficients. A field test is needed to verify the model.