Abstract: During the production of SUS304 austenitic stainless steel welded pipe, after annealing heat treatment, the microstructure changes, resulting in the change of metal conductivity and electromagnetic properties. Based on the differential eddy current testing technology, wavelet transform was used to remove white noise, process the signal and analyze the energy spectrum characteristics of the signal. The results show that with the increase of annealing temperature, the grain size of stainless steel becomes larger, which leads to the decrease of electromagnetic signal energy. By comparing with the results of metallographic examination, the relationship between eddy current signal energy and stainless steel structure is established,which indirectly reflects the annealing temperature of stainless steel pipe and realizes the real-time monitoring and control of on-line annealing heat treatment temperature of stainless steel welded pipe.