Abstract: The constitutive relation of rubber-like materials is important for scientific study and engineering application. However, the fitting ability and reliability of the existing models don't satisfy the requirement. To solve this problem, a new incompressible isotropic constitutive model for the elasticity of the rubber-like materials was proposed in this paper. The form of the constitutive model was studied and a new model was proposed based on plane stress deformation state. This model is an isotropic incompressible model which is defined in terms of the first and second principal stretches and is applicable to describe the elasticity of rubber-like materials in general deformation state. The deformation rules of the material subjected to a lateral constraint was studied and the constraints which this model should satisfy were studied. With a proposed function for stress-strain relation of rubber-like materials under plane stress deformation, a method and a function was proposed to extend the function for plane stress deformation states to a general one for arbitrary three-dimensional deformation states. Thus, a new general incompressible isotropic elastic constitutive model for rubber-like materials was derived. The model was fitted to five groups of test data which all include three types of test and a biaxial test data which covers a broad range of deformation state. The results show that this model fits the test data very well and has a better reliability than the existing models. Besides, the model can predict the material's response well even with a type of test data such as the uniaxial tension test.