After the FeCrNi coatings(with or without NiCrAl adhesive coating)were fractured by the mechanical force, which had been diffusion treated in advance, then the fracture mechanism, the bonding states between coating and substrate and the bonding states inter particles of coating were seriously studied by observing the section SEM morphology on the fracture, and the effect mechanisms of diffusion treatment on improving the bonding strength of coating were also discussed. The coating fracture surface mainly consists of gray area and bright area, layer peeled off brittle rupture, the bonding strength of this way is very lower; Instead, the bright area turns on plenty of"slip-band" and "step-face", with the way mixed with brittle cleavage and plastic slip together.