Laser spot simulation is the important part of target characteristic simulation in hardware-in-the-loop (HITL) simulation system for laser guided weapon jamming. The HITL system composition and laser seeker theory are introduced. Laser spot simulation scheme based on correspondent ratio scaling in similarity theory is shown. Optical system model of laser seeker is established by LightTools, and the sizes of laser spot on detector′ s photosensitive surface in infield and outfield are calculated in different guided time. Laser spot simulation optimization methods based on HITL simulation system for laser guided weapon jamming are proposed. The research result indicates that under HITL condition the size of laser spot on detector′s photosensitive surface is bigger than that in outfield environment, and their changings are not the same. With the distance from the target decreasing, the size of laser spot on diffuse reflectance screen increases and this leads to the increase of laser spot on detector′s photosensitive surface. The result is helpful to improve the precision of laser spot simulation and the reliability of HITL simulation system for laser guided weapon jamming.