In order to study the influence of meteorological elements on the guidance precision of missile under non-standard weather conditions, a type of combined guidance law applied to three-dimensional space is presented and a model of the combined guidance trajectory is established under non-standard weather conditions. An easy-to-program numerical solution of the basic equations of atmospheric motion is put forward and solved through numerical integral method of variable-step four orders Runge-Kutta combining the related differential equations. By way of contrast with proportional guidance trajectory under the standard atmosphere, the result shows that the combined guidance trajectory is closer to actual missile's trajectory.Which directly and vividly exhibits the motion trajectory demonstrating the situation in flying and hitting the target.by STK.