To solve the problem of prediction of multi-axial fatigue life, a new thought and method of establishing multi-axial fatigue life model is proposed. The multi-axial fatigue life model is established by fitting and optimizing axial and multi-axial test data both. This method reduces the restrictions of the formation of multi-axial fatigue damage parameters and the type of multi-axial fatigue test data. On this basis, a new multi-axial fatigue damage parameter based on maximum shear strain amplitude and normal strain and stress on the plane of maximum shear strain amplitude is proposed. The establishing method of multi-axial fatigue life model is evaluated by the multi-axial fatigue test data of ZTC4 cast titanium alloy, pure titanium and BT9 titanium alloy. The result shows that the new method is feasible. The prediction ability of the establishing life model is almost within a factor of two scatter band.