In order to realize the automatic measurement of width of irregular ultra-thin heat pipe, a pixel-by-pixel width search algorithm based on the central axis gradient of machine vision is proposed. First, the Canny algorithm is used to obtain pixel edges, and the improved quadratic interpolation method is further used to extract sub-pixel edges. Then, the thinning algorithm is used to extract the central axis of the enclosed area within the edge and crop it appropriately. Next, to construct the edge of the central axis area by morphological expansion and Gaussian filtering algorithm, to calculate the gradient angle, to approximate the smooth change of the true gradient angle with the help of two-sided mean filtering. Finally, searching for sub-pixel edge points along both sides of the gradient angle, and the edge point pair distance is the target width. It solves the problem that the conventional measurement algorithm cannot determine the width measurement point corresponding to the irregular deformation contour and the high-order transition curve area cannot be measured, and realizes the dense measurement of the width in the axial direction, which approximates the true edge width distribution to the greatest extent. The experimental results show that when the width of measured object is within 10 mm, the measurement uncertainty of the algorithm in the article is ±0.026 mm, which can well adapt to the irregular shape of the ultra-thin heat pipe, and realize stable, reliable, and high-precision automated measurement.