The interlaminar fracture between two dissimilar orthotropic composite materials interface crack problem subjected to symmetric loadings is studied.According to elastic mechanics theories and fracture mechanics knowledge

the mechanics models for boundary value problem to a class of partial differential equations are presented.By introducing special stress functions

we find solutions of eighth order homogeneous linear equation set with complex functions method and approach of undetermined coefficients

deduce calculation formulas of bi-material elastic constants for two dissimilar orthotropic composite materials.The expressions of stress intensity factors near finite interface crack tip subjected to symmetric loadings are derived.A engineering application numerical example is given.The results have certain referential value with respect to practical application and theorial study in related fracture analysis.