The deposition of thin hard coating onto tool steel is done to improve the surface properties such as wear, corrosion. The adhesion strength between substrate and coating is one of important parameters in practical applications since coating failure affects the lifetime of tool directly. Scratch test with acoustic emission(AE) technique was performed to evaluate the adhesion strength qualitative by observing the friction load vs. the normal load curves, the acoustic emission signal generated by the damage of coatings and the scratch track using an optical microscope. In this study, the effect of substrate hardness on the adhesion strength was investigated by evaluating critical load and work of adhesion and observing AE signal and failure mode in scratch track using optical microscope. Coatings were individually deposited on six substrates by means of physical or chemical vapor deposition(PVD, CVD) process and TD process. The critical load of the substrates with nitride layer is higher than without nitride. Although high load causes higher stresses which make flaking occur in the coating-substrate interface, the work of adhesion of harder substrates is also high. Because harder substrates have small contact area causing lower the plastic deformation around stylus.