Detecting information of strapdown seeker was coupled with missile attitude information, so it can't be used for calculating guidance command directly. Based on the downward-looking strapdown homing scheme, the theoretical decoupling model of LOS( line-ofsight) angle from detecting LOS information and missile attitude information was established, as well as its simplified form under rolling stabilizing circumstance. By means of a nonlinear differential filter-tracking differentiator, smooth inertial LOS rate was acquired and a guidance synthetic system of strapdown seeker homing munitions was designed. Trajectory simulation results show that, based on downwardlooking strapdown homing scheme, precise guidance of short-range guided munitions can be accomplished effectively, which has definite value in engineering.