The behavior of reacting shock wave in supersonic premixed flow with the effect of incoming boundary layer is investigated experimentally. A supersonic premixed flow at a Mach number of 3 encounters a ramp, and an oblique detonation wave (ODW) is produced. Four ramp angles (θ) are designed from 36° to 45° (interval of 3 degree) and the equivalence ratio (Φ) can be varied. At a lower equivalence ratio, the ODW cannot be initiated and instead the shock-induced combustion (SIC) comes into being. It is discovered that the overall flow field presents more significant unsteadiness for SIC than for inert shock wave because the separation region is greatly enlarged for SIC due to heat release by chemical reactions in the separation region. As for the ODW, it is prone to propagating upstream after initiated for current experimental conditions. For 39° ramp, the separation region of boundary layer is relatively small, and the ODW presents an abrupt pattern for which a transverse wave exists. However, larger separation region for 42° ramp and its unsteadiness make the transverse wave intermittently appear. For 45° ramp, the even larger separation region makes the transverse wave thoroughly disappear and the ODW presents a smooth pattern.