Abstract: In view of the technical problem that the filter dryer used in air conditioning and refrigerator was easy to leak during service, ZEISS optical microscope, type microscope and Phenom XL desktop scanning electron microscope were used to analyze and compare the test results. The results showed that there were flux components and a large amount of aluminum, iron and other elements distributed in the crack of the filter dryer after welding. It was indicated that the leakage of filter after welding was partly caused by the corrosion of flux and slag inclusion defect. There were obvious cracks and a large number of black slag inclusion in the unused filter dryer, which further indicated that another part of the reason for leakage of the post-welding dryer was due to a large number of defects and stress concentration, leading to the emergence of cracks. The joint action of defects and flux led to leakage in the service process of post-weld filter dryer. The existence of original defects was the source of cracks, and the existence of flux accelerated the expansion of cracks.