Flamelet model and hybrid LES/RANS method were used to simulate SCRAMJET with strut for the Chemical Propulsion of the German Aerospace Center (DLR). The effect of reaction on turbulence was discussed, and comparison between 2D and 3D simulation were presented. The results show the following indication: (1) Mixing is controlled by large eddy scales in nonreacting flow,and the shear layer has three effects obviously； In addition, the combination and pairing of large eddy scales can be seen in 2D simulation, while stretching, distorting and breaking up can be seen in 3D simulation；(2) In reacting case, jet penetration decreases and recirculation zone becomes larger, while, owing to heat release, large eddy scales turn up and saturation appears late. (3) Numerical shadow picture displays good agreement with experimental shadow photograph, while velocity and temperature measurements are consistent with experimental data qualitatively and quantitatively, but 3D model is superior to 2D model in result accuracy.