The invention relates to a method for designing initial tangent line arc heights of main springs of a high-strength two-stage plate spring with gradually-changing rigidity, and belongs to the technical field of plate springs of vehicle suspensions. According to the method for designing the initial tangent line arc heights of the main springs of the high-strength two-stage plate spring with the gradually-changing rigidity, the initial tangent line arc heights of the main springs of the high-strength two-stage plate spring with the gradually-changing rigidity can be designed according to the structure parameters, the elasticity moduli, the contact loads, the idle loads and the rated loads of all the main springs and all auxiliary springs and required design values of residual tangent line arc heights under the rated loads of the main springs and the auxiliary springs. It can be known through simulation and prototype testing, the method for designing the initial tangent line arc heights of the main springs of the high-strength two-stage plate spring with the gradually-changing rigidity is correct, and a reliable technical base is laid for designing of the high-strength two-stage plate spring with the gradually-changing rigidity and development of CAD software. By adoption of the method for designing the initial tangent line arc heights of the main springs of the high-strength two-stage plate spring with the gradually-changing rigidity, accurate and reliable design values of the initial tangent line arc heights of the main springs can be obtained, it is ensured that the design requirements for the contact loads and the gradually-changing rigidity are met, and the design level and the quality of products and the traveling smoothness of vehicles are improved; and meanwhile, design cost and testing cost can be reduced, and the development speed of the products is increased.