Abstract: The cold-rolled steel plates with different Mn contents were hot-dip galvanized in zinc pot with Zn-Al and Zn-Al-Ni bath respectively. The effect of Mn content on the microstructure and thickness of hot-dip galvanized layer was studied, and the solution to over thickness of hot-dip galvanized layer when manganese content was too high was found. The results show that when the composition of zinc bath is Zn-Al plating solution and the mass fraction of Mn in the hot-dip galvanized steel is more than 0.780 0%, the thickness of hot-dip galvanized layer increases rapidly; When the composition of zinc bath is Zn-Al-Ni plating and the mass fraction of Mn in the hot-dip galvanized steel is more than 1.700 0%, the thickness of hot-dip galvanized layer increases quickly; When the composition of zinc bath is Zn-Al-Ni, Ni can reduce its contribution to the thickness of hot-dip galvanized coating by refining the grain size of ζ phase, effectively control the growth of ζ phase, so that the hot-dip galvanized layer with a suitable thickness is obtained.