Based on the theory of fracture mechanics, the maximum stress criterion and the maximum principal strain criterion, the relationship between stress intensity factor and strain energy release rate of I-II-III mixed mode cracks was studied. And the I-II-III mixed mode fracture cracks were simulated by using the finite element software. And the relative error between the simulated value and the theoretical value is, which is within the tolerance range. It is shown that the formula of the relationship between stress intensity factor and strain energy release rate of I-II-III mixed mode cracks is reasonable.