Abstract: A new variable structure adaptive control scheme is proposed.The scheme consists of conventional model reference adaptive control and sliding mode control.The adaptive control based on plant's normalized model can match reference model exactly at the design point.The sliding mode control copes with bounded parameter variations and unmodeled dynamics.Signal synthesis is used as adaptive law instead of the conventional integral law.Through introducing linear zone to sliding mode,the chattering phenomenon is eliminated to a great extent.In comparison with conventional adaptive control,the scheme needs only the plant's input-output mesurements,and has superiority in fine convergence,strong robustness to parameter variation and unmodeled dynamics.The simulation results indicate that this scheme is applicable to aero-engine control.