This paper introduced a kind of reflector mirror support structure of IRST system. The scanning reflector mirror support frame material is Ly2 aluminum under the principle of the suited of material expanding quotient. The support form of the reflector was talked, and the system bracket structure was designed following the requests of the certain complex IRST. The bracket was optimized and analyzed under the best structure quality and the least moment of inertia, and the bellowing of bracket plane thickness, mode frequency restriction and deadweight restriction. From the result we can see that the bracket mass can reduce from 0.73kg to 0.49kg and the moment of inertia can reduce from 0.0109kg㎡ to 0.0056 kg㎡ under the first precondition of the structure mode frequency being low and the biggest transmogrification being teeny. The base frequency and intension of the complex IRST system can be indicated well after the finite element analysis static checking.