Fluid dynamics and mixing transport of an advanced rhombic micromixer with branch channels have been designed and investigated by 3D numerical simulations and experiments. The CFD-ACE+ software was used for simulation and PDMS molding process was used for chip fabrication and experiment. Simulation results showed the advanced rhombic micromixer with branch channels enhanced much high mixing efficiency compared to cross-shape microchannels at the same Re. Compared to the pure rhombic microchannel, the branch-channel rhombic micromixer promoted the mixing efficiency at lower pressure drop at the same Re. Over 90% mixing enhanced by vortices had been achieved at Re > 80. Experimental results show this advanced rhombic micromixer enhances much mixing at Re 60 and uniform mixing at Re 120, respectively. This device is suitable to the application of high-throughput chemical production.