When mechanical components are subjected to multiaxial cyclic loading during operation, the additional strengthening effect is easy to occur. Using uniaxial fatigue life calculation formula to predict their life will produce large errors. However, the existing multiaxial fatigue life prediction models are not convenient for engineering applications because it contains a large number of material constants. To solve the above problems, based on the initiation and promotion mechanism of fatigue microcracks under different stresses, combined with the shear damage model, a new expression of damage parameters is proposed, and the corresponding multiaxial fatigue life prediction model is derived combined with the Manson-Coffin-Basquin equation. The test data of two materials under the non-proportional loading and proportional loading path are used to verify the proposed life prediction model, and compared with the prediction results of the FS model. The results show that the proposed model has a good prediction effect. Finally, the model is applied to the fatigue life prediction of a big pendulum boom, and the results show that the boom meets the fatigue life requirements.