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Nanoindentation testing, also referred to as instrumented indentation testing, is widely used for the mechanical characterization of small volumes of materials. Since the application of coatings in industry has lately increased, accurate determination of the mechanical properties of coatings becameone of the most important concerns for scientists. Complete understanding of the mechanisms of crack initiation and growthseems necessary to determine the sources of error during nanoindentation test. There are few publications in the literature on the mechanisms of interfacial crack growth in the presence of pre-existing defect. Existence of pre-existing defect along the interface between the coating and the substrate leads to sooner initiation of the interfacial crack. One of the important issues that were not mentioned in previous worksis the position of the pre-existing defect and its effect on the failure mechanisms and mechanical properties. In this study we consider elastic-plastic coating on elastic-plastic substrate system and the cohesive zone model embedded in the finite element code is used to simulate the interface between coating and its substrate. The aim of this paper is to investigate the effect of interfacial crack growth in the presence of a defecton deformation behavior and some mechanical properties such as hardness and modulus of elasticity in Cu/Si coating system. Thereason that we choose Cu/Si interface is that experimental results show that the interface between Cu and Si layers in Si/Cu/SiN/Pt/C multilayer coating stuck is the most probable interface to delaminate during the test.