Large eddy simulation was conducted to study the scalar mixing of a 3D supersonic shear layer with convective Mach number 0.62.Governing equations of large scale eddy were solved with fifth-order WENO scheme

and effect of small scale eddy was simulated by using localized dynamic kinetic subgrid scale model(LDKM).The subgrid convective species flux in the filtered species equation was modeled using gradient diffusion method.The results reveal the evolution of the vortex structure of the mixing layer and the scalar field.Simulations show that coherent structures dominate the scalar mixing and the instantaneous distribution of scalar field exhibits obvious 3D characteristics.Statistics such as mean and the root mean square(RMS)of the velocity and the scalar field compares well with the experimental measurements.