By aging of the tunnels with concrete lining, their cracks and defections are also increasing. In old tunnels, spalling becomes a common danger for passing vehicles and trains and frequent monitoring and health check of the concrete lining surface become necessary. Among the non-destructive methods to detect the defects in the tunnel, application of Infrared thermography in tunneling is a relatively new attempt. This study investigates infrared thermography application on the damaged concrete lining of tunnels. The thermal field data of tunnel air temperature and the surface temperature of damaged and undamaged part of several defected lining segments of a tunneling case collected. A thermal numerical model is employed to simulate heat transfer mechanics in this site using the field measurement data. In numerical analysis, convection, conduction, and radiation heat transfer mechanics were taken into consideration and then verified with the field data. The model is used to investigate the influence of temperature differences between damaged and undamaged concrete surface, and also temperature difference between tunnel air and the concrete surface on detection rate of defects.