Abstract: The interfacial structure and properties of the carbon fiber reinforced poly phthalazinone-ether-ketone (CF/PPEK) composites were studied. The interfacial structure of CF/PPEK composite was characterized by XPS and Raman spectrum. And the interfacial properties were discussed through microdebonding experiments. The results show that PPEK resin can form strong interaction with treated carbon fiber at interface，which assures the stress transfer between the matrix and fiber. As a result，CF/PPEK composites have good heat-stability and mechanical properties. A mesomechanical model was presented based on the hypothesis of periodicity in microstructure with continuous and periodic boundary conditions carried out. The interfacial strength of CF/PPEK was analyzed and calculated according to the shear-lag theory and nonlinear FEM method. The results  well correspond with the experiments.