Abstract: To evaluate the spot weld quality of tubule of less than 5mm diameter, the X-ray testing methods are researched. The results showed that the reliable detection of tubule spot welding quality could be realized by twice X-ray testing method of penetrating at vertical weld plane, then turning 90° and penetrating again. As for the defect of about micron level which is difficult to discover by micro-focus digital radioscopy, it can be eliminated by contrasting the result of metallographic examination with continuous optimizing weld parameters.