In laser guided bomb based on velocity principle guided usually a weathercock seeker is adopted to detect the laser energy reflected by the target, calculate the errors between the sight line and guided seeker body line and, then guide the bomb to impact the target. The core element of the laser guided bomb is whether the seeker can detect the laser spot or not. This paper builds up the laser guided mathematical model according to the construction and operating principle of the laser guided seeker, and simulates the process of the seeker receiving the laser spot.