The stress-strain behavior of unidirectional fiber composite under the energy release rate and shear stress criteria for interfacial debonding was simulated based on the proposed nondimensional shear lag analysis in combination with the Monte Carlo method. The main results are summarized as follows. (1) The stress-strain curve and fracture morphology could be described uniquely by the relative strength of the components (fiber, matrix), which is proportional to the ratio of strength of the components to the square root of critical energy release rate in the case of the energy release rate criterion and to the ratio of the strength of the components to the interfacial shear strength in the case of shear stress criterion. (2) With increasing relative strength of components, the number of breakages of the components in the same cross-section decreased, the amount of interfacial debonding increased and the irregularity of the fracture surface increased in both criteria. (3) Because the debonding in the energy release rate criterion grows faster than that in the shear stress one, the damage accumulation process and the resultant fracture morphology were different between the two criteria, especially in the composite with high relative strength of components. (4) In spite of the difference in fracture process between the criteria, the approximate shape of the stress-strain curve was similar because the debonding does not occur unless the component is broken, and therefore the breakage of component occurring intermittently controls the subsequent debonding in both criteria.