Off-axis parabolic mirror is extensive used in non-aberrant targeting by high energy short-pulse solid-state laser. With the incremental requirement for focal energy, the multi-laser focal target is often applied, which puts forward a new request for focusing element. The large-bore tiling parabolic mirror can ensure more that the profile accuracy is over λ/4 and has good augmentability. 90° off-axis design can effectively increase focal efficiency. Based on geometrical optics and diffraction optics, the focal character of 90° off-axis segmented parabolic mirrors has been studied and the misalignment of angle and position are concerned. The results show that the out-of-plane tilt/tip and piston are the main factor affecting strehl ratio and power ratio in a 20 μm-dia meter barrel, discarding the in-plane rotary and decent in active control. The accuracy of tilt/tip and pistion are respective ±0.5 μrad, ±105.3 nm, and the focal performance is predicted by Monte-Carlo tolerance analysis. Under the situation, the ideal focal spot can be afforded for application.