An optical system for a laser apparatus includes: a long-short axis reversing module that includes a splitter, a first mirror, and a second mirror positioned in a propagation path of an incident laser beam, where the first mirror includes a first submirror and a second submirror connected to each other at a predetermined angle therebetween. The optical system converts an incident laser beam having an asymmetric energy distribution into an emitted laser beam with a symmetric energy distribution.