A model to solve the magnetostrictive coefficient of a Giant Magnetostrictive Film(GMF) was established to analyze the coupling relations of GMFs.Then,the building process, deduction mechanism and simulation results of the model were investigated. On the basis of magnetostrictive coefficient expression of a single layer GMF, the magnetostrictive coefficient expression of a composite GMF was obtained by simplifying the deformation of the composite GMF reasonablely.By taking the compound GMF with positive and negative magnetostrictive effects as the research object, the impact of magnetostrictive coating thickness on the deflection of the free end of the cantilever GMF was discussed by using the deduced magnetostrictive coefficient expression. The results show that the deformation capability for both Cu-based thin film and PI-based thin film can reach the maximum when the total thickness ratio of the positive and negative magnetostrictive material layers is 2.3,which realizes the structure optimization of positive and negative cantilevers.