Abstract: Shield machines are essential equipment for tunnel excavation. As a core component of the shield machine, the main bearing plays a critical role, and structural failure of the main bearing can seriously affect the service life of the entire machine. Therefore, it is necessary to accurately calculate and compile the load spectrum of the main bearing to improve the accuracy of its design life prediction.Taking the main bearing of a shield machine used in a practical engineering project as an example, this study analyzes and statistically processes the time-history data of the main bearing using the rainflow counting method. Meanwhile, the main bearing structure is simplified for mechanical analysis, and the calculation formulas for radial load, overturning moment, and axial load of the main bearing are derived. Subsequently, the amplitude loads are divided into ten levels using an unequal interval method, and a ten-level load spectrum of the shield machine main bearing is compiled. The research provides data support for fatigue analysis of the main bearing, which can be used to predict bearing service life, optimize bearing structural design, and improve its operational reliability and durability.