The invention provides a judgment method for defects on a hardening surface of a spur gear of an aero-engine. The judgment method comprises three progressive steps of standard atlas comparison, surface Rockwell hardness judgment and metallography judgment. The judgment method is a progressive and comprehensive judgment method; a judgment result can be quantified; by using the method, the judgment result is unique, and the judgment accuracy is 100 percent, so that the judgment method completely meets the requirement on the quality of the spur gear of the aero-engine and can be popularized and applied to manufacturing of gear surfaces with hardened surface in the fields of aerospaces, ships, automobiles, petroleum and the like; meanwhile, a technical reference is supplied to the research on other types of aero-engines.