In this paper we adopt a new technique combined with operator theorem to analysis linear time-varying system. This make us solve the robust control problems of linear time-varying system more easily. Also, we can apply this method to the problems of linear time-invarying system. First, we construct the operator we want to use, then apply it to the linear time-varying system. Moreover, we can apply this method to the structure singular value problem of robust control, and the result is similar with the linear time-invarying system. Then , we construct the standard control problem , and adopt linear matrix in- equality to get suboptimal controller to satisfy the robust performance we need. Finally,we use numerical method to discuss it.