To provide valuable references for practice，a finite element analysis software ANSYS is used to simulate non-destructive testing(NDT)of internal crack in straight seam welding pipe by electromagnetic exciting infrared thermography.The mathematical model of electromagnetic field and temperature field is built according to the induction heating principle.The order coupling analysis of two fields is conducted，and the influence of internal crack of welding pipe on detection law are discussed through changing the buried depth，coil position，materials and induction heating time.The results indicate that internal crack influences the temperature of specimen surface，and the surface temperature decreases with increase of the buried depth and coil eccentric distance.Besides，the ferromagnetic material is more likely to be detected.The existence of internal cracks can be detected by selecting the appropriate excitation frequency or current intensity and the coil position.