Abstract: The technology about detection, reconnaissance, and guidance of IR imaging occupies an important position in modern war. In order to quantitatively evaluate the obscuring effect of smoke agent and smoke equipment to IR imaging system, the test process and calculation method of some characteristic parameters were discussed in detail. Both the mass extinction coefficient() and the total obscuring capability(TOP) were characteristic parameters to evaluate the obscuring performance of smoke. And their comparatively accurate test results could be got in the smoke chamber where distribution of smoke particles was easily uniform. So the smoke agent could be selected on the basis of the mass extinction coefficient and the total obscuring capability. Nevertheless, in the field experiment, the motion state of smoke particles was strongly affected by meteorological factors. Then it was very difficult for and TOP to be directly measured. So the obscuring efficiency of smoke agent and smoke equipment to IR imaging system had best be quantitatively characterized by other parameters, such as the transmissivity and the effective obscuring time.