Wettability of Zn-Al alloy melt on the pure iron substrate at 450 ℃ was studied. The effect of Al content (Zn, Zn-1Al, Zn-2Al, Zn-3Al, Zn-4Al, and Zn-5Al) on the wetting behavior and interfacial reaction was investigated by high-temperature contact angle measuring device and scanning electron microscope (SEM). The results show that, with the increase of Al content, the initial contact angle of the molten alloy on the substrate decreases gradually and the wettability increases gradually. Compared with the initial contact angle, the final contact angle is slightly reduced, because the Fe-Al inhibition layer is preferentially formed at the interface when adding Al to the alloy. The presence of Al will promote the occurrence of the reactive wetting, leading to an insignificant wetting spreading process, and the final contact angle negligibly differs from the initial contact angle. The adhesion work and charge density distributions of interface systems were calculated based on the first-principles. The results show that the adhesion work of the Fe/Zn and Fe/(Zn-Al) interface model is 2.0171 J/m2 and 13.7944 J/m2, respectively. The addition of Al greatly increases the adhesion work between alloy melt and iron substrate. Compared with the Zn-Fe and Al-Fe interface models, it can be seen that a significant charge migration phenomenon occurs between the interfaces. The amount of charge migration in the Al-Fe interface model is much larger than that in the Zn-Fe interface model, indicating that the bonding between Al-Fe atoms can occur more easily and the interaction between Al-Fe interfaces is stronger. This is also the reason why the addition of Al increases the adhesion work between interfaces.