In the case of image gray distribution without significant double peaks and the complex background, the dynamic image segmentation method combined with global threshold has good adaptability. The global threshold of near-infrared image s, and the threshold value of the small-block images d are evaluated by the method of OTSU, and the threshold matrix D with the original image by the bilinear interpolation algorithm. Finally, the structure of threshold matrix T and segmentation of image are completed by adjusting the scale coefficient k. This method can effectively split images of the furnace tube in petrochemical refinery.