Abstract: A smart layer was developed by effectively overlapping continuous carbon fibers in a local area in epoxy matrix. The smart layer was stuck on the st ructure surface to sense its deformation and perform a large-region monitoring. Based on the smart layer, the strain and displacement of the components were detected in the uniaxial tension and three-point bending experiments. The results indicate that the local overlapped structure is the essence of the overlapped carbon fiber polymer-matrix smart layer. The gauge factor of the overlapped carbon fiber polymer-matrix smart layer, defined as fractional change in resistance per unit strain, is as high as 104, which is 34 times as that in continuous carbon fiber composites without an overlapped part. The results further show that the piezoresistivity curve of overlapped carbon fiber polymer-matrix smart layer is smooth and stable, and exhibits a sensing limit of around 8500 με. An electrical model of the overlapped carbon fiber polymer smart layer was established, which revealed that the change of interlaminar resistance in the overlapping region is the source of its piezoresistivity. Furthermore, a preliminary explanation of the mechanism of the change of interlaminar resistance was made from fiber axial load, overlapped area and interlaminar shear strain.