The propagation and translation of the ghost beam in the high power laser system were analyzed in detail by theoretical calculation and experiments. The position of ghost image and the mitigating measures were studied in the preamplifier system of high power laser facility. A number of mitigating measures, which included tilting of lenses and choosing the meetingsurface of lenses, were implemented to avoid the risks of optic damage from the ghost image. And with the technology of suppressing the pencil-beam and back laser,the steady and reliable output with the improved SNR was gotten.