The detecting welding seam has been a difficulty problem in pipe manufacture for a long time

this paper proposed a new method for it based on the wavelet transform theory and its technology of edge detection. The method mainly relates to the pretreatment of the seam image

the wavelet transform based on three order spine function

the scale parameter effect on the transform results and the correlation analysis on the ultimate results. By the analysis on the theory and the simulation on computer

the method shows higher estimated precision and better capability of anti disturb. In the other hand

its complication is not high. So it can be used into real time control system.