Abstract: In this papers mixed mode fatigue crack growth is studied in detail. A new fracture mechanics equipment composed of CTS （compact tension and shearing） specimen and its special loading device is used in the experiment. The direction of crack propagation in the experiment is explained with several theories including the Minimum Plastic Radius Principle and some interesting results are obtained.Based on the linear theory of elastic fracture mechanicss the generalized J integral theory is discussed and used to predict the mixed mode fatigue crack growth. The fatigue crack growth model is presented as:which involved not only the crack growth rate, but also the direction of the growth. In mode I cases it can be changed into a form similar to that presented by Erodogan and Walker as well as Broek and Schijve.By using the above equation and standard 12-nodes elements, numerical analysis is carried out to predict the crack growth in the CTS ex peri ment. The results are satisfactory. Also the strain energy density factor theory is used for fatigue crack growth prediction, and the result is compared with that of the above theory. Besides,the influence of -K2 component on the crack growth rate is discussed qualitatively.