A method for detecting the image edge of V-groove and calculating the welding deviation was presented.The cubic spline wavelet was used to transform the image to recognize the edge,in order to outstanding the edge and weakening the noise,the wavelet transformatinon on scale 1 and scale 2 was multiplied each other for recognizing edge of V-groove condidently,and finally the mathematics mold was established to compute the welding deviation.The results show that the image processing is simplified and operation is reduced by this method.It can match the real-time signal processing in the welding automatization.