Compact tensile shear（CTS) specimens of TC4 diffusion bonded joints were designed and processed. The fatigue crack propagation tests of Ⅰ-Ⅱ mixed mode under different loading angles were carried out. The test results showed that when the loading angle was less than 45 degrees

the cracks propagated along the weld line. When the loading angle was more than 45 degrees

the cracks started to propagate along base metal at certain angle. The a-N curves of crack propagation were obtained by electron microscopy in combination with potential method. Based on the test results

the interaction integral method was used to calculate the stress intensity factor

and the Ⅰ-Ⅱ mixed crack propagation process was analyzed based on the strain energy release rate. Finally

considering the weight of crack mode Ⅱ

the composite ratio was introduced. On this basis

a unified model of Ⅰ-Ⅱ mixed crack propagate rate of TC4 diffusion bonded joints under different loading angles and loads was established.