Abstract: The characteristics of lateral concentration distribution in a pollutant contained impinging jet in the downstream region related to the stagnation point in flowing water are numericaly investigated in detail using the RNG turbulence model,and compared with the corresponding experimental results. The formation mechanism and diffusion properties of the lateral high-concentration convergence zones in the downstream transition region are analyzed. The computed results indicate that the impingement action and the circumambient cross flow play an important role in the lateral concentration distributions of the impinging jet in the transition region. When the velocity ratio is relatively smal,there exist distinct lateral high-concentration convergence zones both near the symmetry plane and at the lateral edge between the botom layer wall jet and the ambient cross flow,which are dominated by the lateral negative pressure gradient produced by the impingement act ion and the Scarf vortex structure generated by the circumbient cross-flow,respectively.