Abstract: The internal drag trait of three-dimensional sidewall hypersonic inlet(before the throat) has been investigated by numerical simulation,streamline tracing and constant dynamic pressure of incoming flow(variation of Ma=4.65～6.65).The results show that: 1) Pressure drag and total drag on the internal walls decrease when the Ma increases,but the friction drag on the internal walls increases when the Ma increases and the ratio of friction drag is less than 20%.2) Thrust efficiency and thrust and drag ratio increase with the increase of Ma.Thrust efficiency increases by 13.8% and thrust and drag ratio increase by 2.73.3) Additive drag decreases when the Ma increases and the additive drag actually becomes "additive thrust" at high Mach number.