Abstract: In order to improve the filled factor of beam and the conversion efficiency of amplifier, with reference to the technical integrated line of Shenguang-Ⅲ, a kind of new spatial four-pass amplifier structure is designed, which is made up of four pairs of spatial filters, in the Ti:sapphire CPA system. The spatial structure amplifier is put in a vacuum because there are real focus points in the amplifier. Before amplification, the input Gauss beam firstly goes through a diaphragm and then a static spatial filter with a pinhole, the beam is refitted into a 4th order super-gaussian beam. Then, the image of super-gaussian beam is relayed to the first spatial filter of amplifier. The Ti:sapphire crystal is put at the surface of image or object of the spatial filters for the sake of the good qual