In Fig. 7(a), it can be seen that the trend of micromixer G-B is the closest to the original curve (G-B-G). It means that the effect of G2 is weak compared with G1 or the baffles. The worst performance is found in the mixer B-G, thus the influence of the gap G1, i.e., the contraction and expansion effect at the very beginning, on the mixing efficiency is very significant. At Re = 40, the mixing efficiency of micromixer B-G is 63.7%, while the mixing efficiency of micromixer G-B-G is 94.3%. Mixing efficiency is increased by 48%. According to the data in Fig. 7(b), the contribution of the gaps to pressure drop is larger than that of the baffles.The pressure drop of micromixer G-B decreases by 42% compared to micromixer G-B-G at Re = 60.