The micromixer is a key component of the microfluidic chip analysis system. Micromixers are widely used in applications, such as DNA hybridization and protein synthesis. A high-efficiency mixer can speed up the biochemical analysis process. In order to study how to improve the mixing efficiency of the mixer, this paper designs passive micromixers with three different blocks: cylindrical, equilateral triangle, and square. The effects of them on the mixing performance and pressure drop of the mixer were studied, respectively. Through numerical simulation, the study shows that the mixing efficiency of the mixer with equilateral triangle blocks is 96% at Re = 100, and the maximum pressure drop is 18 135.8 Pa. In addition, through the analysis of three-dimensional numerical simulation, the block causes the fluid to generate a horizontal and vertical vortex flow state in the mixing unit, thereby breaking the laminar flow and greatly improving the mixing efficiency. Through structural optimization, ETOM4, which has four mixing units and a side length of 150 μm equilateral triangle blocks, is the best passive micromixer with its mixing efficiency of 99.1%.