Transmission lines across the houses or greenhouses, etc., the electric field is unevenly distributed due to the distortion of complex environment. Therefore, the accurate measurement of the electric field in the narrow area of the sensitive point has become the key problem in the research of electromagnetic environment. At present, the research on the principle and system of non-uniform electric field measurement is relatively few. Based on the existing system measurement principles and methods, a non - uniform electric field measurement system for small space measurement is designed for the three pairs of the spherical top and the X, Y and Z axes that through the analysis of the influence of the two measuring systems of sphere and box on the electric field. The calculation method of non-uniform electric field is analyzed by using the principle of the measurement of the electric field of the suspension body. The simulation verifies that the measurement error of the non-uniform electric field is within 10%. The actual measurement error of the measurement system is within 8%, which effectively verifies the accuracy of the measurement system for the measurement of the non-uniform electric field.