The mechanism of erosion phase transition of Fe2Al5 coating in molten zinc was investigated. Experimental results indicated that etched grooves caused by interfacial tension equilibrium driving formed on sample surface. The Fe2Al5 phase, on where zinc did not adhere at the early stage of erosion, was infiltrated by zinc and solid solution Fe2Al5-Znx (η phase) was formed due to zinc atoms diffusing into Fe2Al5 phase. The erosion process of Fe2Al5 in molten zinc is directed melt at the interface caused by phase transition to drive. There were three types of phase interface，η/L,η/(η+δ)/L and η /(η+δ)/δ+L，formed in corroded area .The solid (S) / liquid (L) interface was phase-equilibrium interface and the S/S interface like η/(η+δ) and (η+δ)/δ were non phase-equilibrium interfaces at erosion temperature. The demand of phase-equilibrium interfaces and phase transitions of non-equilibrium interfaces, η→(η+δ) and (η+δ) →δ, made the S/L interface move towards to solid phase and Fe2Al5 phase was corroded by molten zinc.