Abstract: The structural failure of the main bearing, the core component of the shield machine, will seriously affect the life of the shield machine. The shield machine is an important equipment for tunnel excavation. It is necessary to accurately calculate and compile the load spectrum of the main bearing to improve the accuracy of the design life of the main bearing. Taking the main bearing of a shield machine in a practical project as an example, the time process of the main bearing is analyzed and counted by the rain flow counting method, the main bearing structure is simplified, the force analysis of the main bearing is carried out, and the calculation formulas of the radial load, overturning moment and axial load of the main bearing are calculated. The amplitude load is divided into ten levels by the unequal spacing method, and the ten-level load spectrum of the main bearing of the shield machine is compiled.Provide data support for bearing fatigue analysis and predict the service life of the bearing. Optimize bearing design to improve working reliability and durability.