Abstract: During the periodic inspection for in-service power plant boiler, magnetic particle testing was used mostly for the inner and outer inspection of the pressure vessel parts. Combining the relative requirements in standard JB/T 4630.4—2005, the magnetic particle testing procedure and practice operation technique for the weld inspection during the inspection were deeply analyzed to improve the detection efficiency for the surface defect. And combining the standard, the proceeding methods for detected defects were discussed.