Measurement of the electrostatic field generated by moving object is an important problem in electrostatic field research. Those common non-contact measuring methods are not suitable to measure this kind of field. A method based on three-dimension measurement is discussed in this paper. Three potential differences is gained when three pairs of paralleled poles perpendicular to each other locate in the electrostatic field, and then the amplitude and the orientation of the electrostatic field can be calculated exactly. It is proved in simple test with a self-made electrostatic detector that this method can be used in measuring the electrostatic field of moving charged object.