To minimize the subjective factor in the application of backscattered electron imaging and image analysis(BSE IA), a reliable method of pore threshold was proposed. Besides, the formula of minimum number of frames needed to determine the analytical result was deduced. The influence of determination methods of pore threshold and image magnification on the test results has been analyzed. The results showed that the test result of measurement by using the second derivative of cumulative distribution curve of grey area to determine the pore threshold and 500 magnification backscattered electron image was not only reasonable but also moderate workload. Compared with the results of mercury intrusion porosimetry(MIP), porosity measured by BSE IA technique was smaller. But BSE IA had a unique advantage in the characterization of pore structure of cement based materials for that it can directly observe the shape and distribution of pores.