Bi-material cantilever is an important element in a heat energy sensor for its thermal-mechanical character. The cantilever based on silicon process is usually made of metal and non-metal films. To improve the reliability of the cantilever, an adhesion layer is often needed between two films which do not adhere steadily each other. For analyzing bi-material structure with an abhesive layer in between, according to the theories of thermal stress and combined deformation on mechanics of materials, a tri-layer material cantilever model was set up related to the physics properties of materials, the structure dimension of cantilever, and the tilt angle caused by thermal stress. The material selection, the thickness, and the thickness ratio determination of a tri-layer material cantilever were analyzed by this model. Based on silicon process an optic readout infrared focal plane array(IRFPA) was designed, fabricated, and tested. The results show that the model is practical and accurate enough. The model was also verified by a finite element simulation.