Abstract: Multiaxial fatigue is a common issue encountered in fatigue failure of rubber isolators. The portion of Strain Energy Density (SED) to initiate crack growth under multiaxial fatigue loads is defined as the Cracking Energy Density (CED). Using the measured fatigue crack growth characteristics of rubber material and the calculated CED of rubbers under external loads, one can predict fatigue life of rubber components. The key issue using this estimation method is to calculate the CED of rubber components under external loads. To calculate CED using the output strain from the finite element software (ABAQUS) as input data, the formula for CED under the principal coordinate system and the integral technology are proposed. Six hyperelastic constitutive models for rubber materials are included into this method for calculating CED. Taking some typical strain states (uniaxial tension, planar tension and simple shear) as examples, the CED calculated from the proposed formula is compared with the corresponding SED. The comparisons validate the proposed method for calculating CED. Finally, the CED developed using the method proposed is used to predict multiaxial fatigue life of rubber isolators.