Relationships among the three expressive values of diesel engine smog emission, such as Bosch smog value, extinction coefficient value and smog mass concentration value, were established by means of mathematical analysis method. Every two expressive values have higher relativity. In order to validate the calculation accuracy, the smog emission of three kinds of automotive diesel engines was tested. The comparative results of experiment and calculation showed that the formulas used to make calculation between Bosch smog value and extinction coefficient value are able to get a high accuracy. When diesel engine operates at higher load operating condition, the particulate matter emission can be calculated accurately by the formula between Bosch smog value and particulate matter concentration, but there is some calculation error as the engine load is lower. At lighter load operating condition of diesel engine, there is a lot of soluble organic fraction in particulate matter, but Bosch smog meter is only able to measure the black degree of filter paper. 