A detection method of crack infrared thermal image based on tensile sensitive effect of polymer conductive films was proposed. The results show that under external power excitation, conductive particles in the conductive film coated on the surface of concrete form conductive pathway due to tunnel effect. Temperature field of local thermal effect on the surface of concrete crack can be shown with the result that crack location and direction are shown by infrared thermal image. Crack accuracy of detection is 0.04mm. Crack width scope of detection is among 0.040.30 mm. Detection distance reaches 40 m. Concrete crack can be detected rapidly in large areas by distributed monitoring in remote, non contact way.