Carbon steel is widely used in many fields.It is of great importance to study the behavior of carbon steel in nondestructive testing.To investigate the behavior of carbon steel in thermal pulse video thermography nondestructive testing,two standard carbon steel test-pieces are made.The sizes and depths of defects in two standard carbon steel test-pieces are studied by thermal pulse video thermography.The results show that for the purpose of minimizing errors of size measurements the testing time should be chosen at about 0.3 s after the thermal heat flux applied to the specimen with defects of smaller depths （l〈1.8 mm ） and it is more difficult to measure the size of shallower defect than that of deeper defects.For the defects with diameters larger than 6 ram,the depth measurement errors are usually small if the thermograms are in high contrast.If defect diameters are smaller than 6 mm, the depth measurement errors are usually more than 10% .To determine the depth of the defect it should be performed shortly after the thermal flux applied to the test-piece to avoid the blurring of the thermal images due to heat diffusion.