Abstract: The sensor characteristics of CFRP unidirectional laminates were studied by measuring the resistance changes while tension or cyclic tension was applied. The results show that the characteristics of resistance change are different at different ply angles. These characteristics can reflect more information than stress and strain. It is found that CFRP unidirectional laminates have piezoresistive effect. With an increase in stress,the piezoresistive effect increases. The piezoresistive effect of off-axis and 90° CFRP laminates is strongerthan that of 0° CFRP laminate and with the increase of the ply angle the piezoresistive effect increases. By useof the characteristics of resistance change, the CFRP unidirectional laminate can be inspected in-situ and the damage can be diagnosed by itself.