In order to embody effective range of smoke bomb, the concept of effectively obscuring region(EOR) of smoke-screen was proposed, and the calculation model of the EOR posed by smoke screen for millimeter-wave terminal guided radar( MMWTGR) was present by means of calculation of smoke surface density and obscured surface density of MMWTGR posed by smoke bomb. The VC + + simulation was used to analyze changing rule of the EWR under different conditions so as to obtain some useful characteristics of smoke bomb obscuring. Several conclusions have been reached, for example, the maximum obscuring direction of the smoke-screen is the direction of the line from target to the smoke bomb. At the same time, correctness of expressing effective range of smoke bomb by EOR was verified.