This paper deals with the problem of designing a robust controller with adaptation mechanisms for the purpose of improving transient performance in time-response. The controlled object is a linear system with unknown parameters which vary within certain prescribed bounds. In the proposed method, a target model with adjustable parameters is constructed in order to obtain on-line information on parameter uncertainty and to improve transient time-response. A robust controller is established in a parameter-dependent form, in which parameters are adjusted on-line on the boundary surface of the possible parameter space according to the error between the state trajectory of the plant and that of the target model.