Abstract: 100 m high speed heavy rail belongs to high carbon steel, and decarburization is easy to occur on the surface during heating. The depth inspection of decarburization layer is one of the most important inspection items of 100 m high speed heavy rail. TB/T 2344-2012 standard stipulates that the depth of decarburization layer shall not be greater than 0.50 mm. The inspection method of decarburization layer specified in this standard is different from that specified in GB/T 224-2019 standard. The depth test method of decarburization layer in TB/T 2344-2012 standard is to measure the depth from the sample surface to the continuous closed ferrite mesh. In GB/T 224-2019, the inspection method of decarburization layer depth is to determine the average value from the sample surface to the deepest depth of decarburization.