Since multi-band high-energy laser emission window′s diameter is large, single ZnSe lens can′t satisfy the working requirements. A window splicing method is proposed. According to the equipment′s actual stress, the window′s strength is calculated to make the window′s design more reasonable and reliable. The window′s boundary conditions is acquired through analysis of the equipment′s work environment and further detailed analysis by using finite element software is done to study laser emission window′s mirror deformation under the effect of thermal coupling force. Then, fitting of inner and outer surface of the window by Zernike polynomials is carried out to obtain the Zernike expressions of the window′s surface shape. The window′s influence on the beam while working in complex environment is analyzed from the view of beam divergence, times of diffraction limitation β and fractional encircled energy RBQ by Matlab. The results show that stitching can greatly reduce the cost and quality of the window and the impact of laser beam is fare, it can meet the equipment requirement.