The invention relates to a simulation calculation method for pre-clamping stress of equally-thick main springs of two-stage gradual-rigidity leaf springs, and belongs to the technical field of gradual-rigidity leaf springs of a suspension. Through the adoption of the method, according to the number of the main springs, structural parameters of each equally-thick main spring, a design value of height of each free tangent arc and elasticity modulus, simulation calculation can be performed on the pre-clamping stress of each equally-thick main spring after assembly and clamping of the two-stage gradual-rigidity leaf springs. Prototype testing proves that the simulation calculation method for the pre-clamping stress of the equally-thick main springs of the two-stage gradual-rigidity leaf springs is correct, accurate and reliable simulation calculation value of the pre-clamping stress can be obtained, and a reliable technological method is provided for simulation calculation of the pre-clamping stress of each equally-thick main spring of the two-stage gradual-rigidity leaf springs. By means of the method, the pre-clamping stress of each equally-thick main spring can meet the design requirement, design level and reliability of the product as well as vehicle traveling safety can be improved, and service life of the product can be prolonged; meanwhile, design and testing expenses of theproduct are reduced, and the product development rate is increased.