The focus mirror is a cell of space camera structure’s design. The imaging quality of space camera depends on its structure design directly. Based on a wide cover camera, the focus mirror has long figure of length-breadth ratio 3:1, which makes the design of supporting structure more difficult. For insuring the imaging quality of focus mirror optical surface all the time, the flexible supporting structure has to be provided with dynamics and statics, as well as smaller mass, higher ratio-rigidity, well machining and assembling capability. By analyzing, focus mirror with the flexible supporting structure can meet quality targets, whose surface quality is 1/50λ and first mode is 275 Hz.