Disclosed is an excimer laser composite cavity, comprising a laser discharge cavity, a laser output module, a line-width narrowing module, and a laser amplification module. The laser discharge cavity contains work gas for generating laser when it is activated by an excitation source. The laser discharge cavity, the laser output module, and the line-width narrowing module constitute a line-width narrowing cavity configured to narrow down a line-width of the laser generated by the work gas. The laser discharge cavity, the laser output module, and the laser amplification module constitute an amplification cavity configured to amplify power of the laser with the line-width having been narrowed down by the line-width narrowing cavity.