Porosity is one important characteristic feature and structural index of sprayed coatings. A method of measurement of porosity, EPMA-EDS image processing is developed in the paper. The characteristics of pores can be determined by processing of the image obtained from an electron microscope via VISTA, Not only the porosity can be presented but also the statistical result of pore size distribution. Finally it can be drawn from this paper that EPMA-EDS is a quite effective method to completely characterize the pores in plasma sprayed coatings.