Bellows type air spring is a kind of strong nonlinear resistance elements and its loadbearing and its stiffness both can be adjusted by internal air pressure. Its characteristics of loadbearing and stiffness characteristics not only depend on air pressure, but also on its geometry and shell material property. According to the special structural properties of the bellows air spring and using the formula for rotator volume, the calculating formula of its inside volume changed with the compression displacement and the capsule air pressure were deduced. The mathematical model of load force changed with the compression displacement and theoretic characteristic curves were established based on state equations of ideal gas. The nonlinear relationship and changing trends between load force and compression displacement were verified by compared the actual loadcompression changing characteristic curves of displacement and the theoretic curves. The decuded calculating formula of load forcedispalcement compression with different initial inflation pressure provides a theoretical basis for the selection and design for air spring.