An improved edge thinning method with adaptive smooth filter is proposed for de-noising and thinning rough edge detected by Sobel operator.A new gradient operator is used for adaptive smooth filter，which can overcome noise influence and sharpen image edge effectively.Then，the improved edge thinning method is used after edge detection with Sobel operator.Experimental results show that the new gradient operator is better than the old one with the same iteration number，and the improved edge thinning method can preserve more edge details with a considerable calculation time meanwhile.