Understanding the wetting characteristics of a droplet on a solid surface is an important topic in basic research and various engineering applications. The further understanding of wetting characteristics of working fluid is very valuable for revealing the mechanism of phase change heat transfer, especially for understanding the complex phenomena of phase change heat transfer of mixtures. In this study, the wetting behaviors of R32, R1234yf, and R32/R1234yf nanodroplets on square pillar-type substrates were investigated by molecular dynamics simulations. The influences of structure size, droplet composition, and droplet size on the position of the critical line were investigated in particular. The results show that the droplet tends to be the Cassie state with higher pillar and shorter spacing. The influence of droplet composition on wetting state conversion is approximately linear with concentration. The influence of droplet size is relatively small. The results are reasonably explained by the force analysis method proposed in this paper.