The planetary carrier is an important transmission mechanism in tracked vehicles side gear reducer,and it is designed with the static strength theory within the limitation of test and experimental method.Thus the actual dynamic characteristics of planetary carrier cannot be embodied,and it brings difficulty to predict life with given dynamic loads and results in wide gap between actual life and designed. The virtual running test platform is built based on ADAMS. ATV,and the dynamic load suffered by planetary carrier in different working condition is obtained. Then the fatigue life of planetary carrier is obtained with the fatigue life prediction model of planetary carrier established with MSC. Fatigue. The study case proves the new method is feasible to predict fatigue life of planetary carrier,and the fatigue life prediction for tracked vehicles component under complex operating conditions are explored. The study results can widely extended to other engineering domains,and it has very important practical significance.