Rapid mixing is essential in biochemical analysis, drug delivery, biomedical inspection, as well as RNA and DNA synthesis and testing. A suitable evaluation method is required for mixing effect comparison in the stage of research and development of mixers. Until now, no satisfactory method was developed to quantitatively evaluate the mixing performance of micromixers. We describe an inspection algorithm that uses image gray level to evaluate the mixing effect in micromixers. Computer simulation results show that the mixed range and the mixing concentration can be recognized. Experiments are implemented in a self-designed two-channel micromixer, in which the diameter of the mixing chamber is 1 mm and height is 200 µm. Experimental results show that the proposed algorithm can clearly display the full-field mixing state in the mixer, so that it is helpful to evaluate the performance of a micromixer. In addition, a mixing efficiency over 90% is obtained within 0.35 s at a flux of 7.81 µl/s in the self-designed mixer. Since the purpose of rapid and uniform mixing is obviously achieved, this mixer can be applied to the field of biomedical diagnosis.