Increasing applicable scope of Reynolds number and mixing strength is development trend of micro-mixer design. A passive-type micro-mixer of 3D-asymmetrical rhombus was designed and manufactured on the basis of asymmetrical separation and reconstruction mixing principle, and change of mixing strength and mixing state were studied by means of numerical analysis and visualized experiment. Results indicate that in scope of low Re (0.01~10), the mixing between two components is dominated by diffusion mixing, with increase of Re, the influence of flow speed on mixing strength decreases to a certain degree; in higher scope of Re(10~200), influenced by increase of flow speed, the inter-fluid imbalance inertia collision becomes the main factor affecting mixing, and mixture strength gradually increases and tends to be stable with increase of flow speed. Take the micro-mixer with Re scope of (0.01~200) as research object, influence of structural sizes such as width slit ratio W/sS, divided-compound angle θ, width-to-thickness ratio H/S, etc on mixing strength was analyzed. By taking into consideration of fluid mixing strength and change of passage pressure drop comprehensively, the optimum structural size of passage was designed as Ws/S=0.2, θ=45°, H/S=0.5, and mixing strength of micro-mixer can maintain above 78%. Compared with traditional planar symmetrical separation-and-reconstruction mixer, mixing strength of designed passive-type micro-mixer of 3D-asymmetrical rhombus is greatly increased, which verifies the effectiveness of the structure.