The electrostatic precipitator with longitudinal transverse collecting plates had better characteristics. The theoretical correlation for the calculation voltage, which was produced by space electric charge in the ESP with longitudinal transverse collecting plates, was deduced in this paper. Not only the electric potential, but also the calculation formula of strength of electrostatic field，were established on the basis of image charge methods. The measure results of both the electric current density of collecting plate, and the average strength of electric field of collecting plate, were consistent with individual electric field intensity distribution. These indicated that the inference course was credibility.