Abstract: X ray crawler in long distance pipeline girth welding seam X-ray detection is widely used. During the application in the second west to East Gas Pipeline Project of large diameter pipeline, partial target phenomenon was observed for circumferential conical target X ray generator, causing the circumferential X ray intensity inhomogeneity and film densiting difference. To solve this problem, the focusing coil was used in the circumferential conical target X ray generator to correct the trajectory ofelectron beam. Through the analysis of the experiment, circumferential field intensity reached the purpose of uniform. Application in the follow-up of the long distance pipeline construction in radiographic testing received good results.