Abstract: The coating structure of 20 steel whole hot-dip aluminizing heat exchanger tube was analyzed,and the hardness and thickness of dip aluminum coating was measured .The result showed that the dip aluminum coating was composed with pure aluminium layer and iron-aluminum alloy layer.The coating was uniform and well-adherenced to the matrix,and the coating thickness was 50~125 μm,the alloy layer thickness was 37~83 μm. The coating thickness of weld joint was thinner than matrix. The average hardness of iron-aluminum alloy layer was 884.8 HV0.02. Its leading composition was FeAl3 phase.