This work presented a multi-component LBM approach to model the scalar mixing process with the chemical reactions in a liquid system. Two-dimensional simulation was applied to investigate the enhancement of the mixing performance at the laminar flow regime with very low Re numbers. The mixing degree measured with both IOS (intensity of segregation, characterized by the pure mixing without reaction) and X-S (segregation index, characterized by the chemical reaction) was used to quantify the mixing performance. The investigation in both pure mixing process and the reacting flow system showed that the flow-focusing effect with the simple geometry could significantly enhance the mixing as well as the subsequent chemical reactions at very low Re numbers. We expected the theoretical approach described in our study to provide an effective method for micro-device design and optimization. (C) 2012 Elsevier Ltd. All rights reserved.