The method of computational fluid dynamics (CFD) was used to carry out numerical simulation study to 2D flow field in wide and shallow region with a non submerged spur dike. The simulation results show that the RNGk-ε model can better describe the actual water characteristics around spur-dikes, the recirculation diffusion and disappearing process，and simulate the recirculation scale. The flow structures with different inlet velocities under the same conditions were simulated with the model. Through dimensional analysis and comparative analysis of numerical simulation results, the paper got the relation of inlet velocity and recirculation scale.The larger the inlet velocity, the longer and wider the recirculation sideline. The research result has a certain reference significance for the design and construction of spur dikes.