The generation and expansion of cracks in galvannealed coating were analyzed under the condition of compressive or tensile stress, and the interaction between the coating and the steel substrate was analyzed during galvannealed deformation by environmental scanning electron microscope （ESEM） with in-situ investigation method in tension test and three point bending test. The results showed that the damaging process of the galvannealed coating under tensile stress could be divided into two stages. In the first stage the major damage form was powdering, in the second stage, the major damage form was flaking. Under the composite tensile stress, the fracture of galvannealed coating was not along with the fixed interface but arised with different types of fractures and flakes at different stages of the loading; and the interface fracture was different in different regions. When the galvannealed coating was subjected to tensile stress, cracks occurred at the Г/δ interface and extended perpendicularly to coating plane in the 3 phase, and then propagated along with the Г/Fe interface. The signs of plastic deformation of coating was not obvious under tensile stress, but showed apparent plastic deformation under compressive stress. During the deformation of coating and steel substrate, there was substantial interaction and inhomogeneity.%用配备拉伸／三点弯曲试验装置的SEM原位观察分析了热镀锌合金化钢板变形时镀层中裂纹产生、扩展、镀层断裂及在塑性变形过程中镀层与钢基体界面的交互作用。结果表明，在拉应力作用下，镀层的破坏可以分为两个过程：第一阶段主要表现为粉化；第二阶段主要表现为剥落。镀层在复合应力作用下的断裂并非沿着某一固定的界面发生，而是在载荷作用的不同阶段，发生不同类型的断裂和脱落，在不同区域镀层断裂的界面不同。当镀层承受拉应力时，裂纹在Г／δ相界面产生，在艿相中沿着垂直于镀层平面的方向扩展，并沿着Г相／钢基体界面延伸，镀层塑性变形的
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