Aiming at the problem that the shield guided laser spot cannot be accurately recognized due to the interference of stray light in the construction site. To address this issue, an anti stray light algorithm based on the digital image processing is proposed, which utilizes the pulse characteristics of guided laser. Firstly, the relationship between the exposure time of the industrial camera and the laser pulse period is analyzed. Two images before and after the guided laser pulse can be effectively acquired in the stray light environment by adjusting the exposure time of the industrial camera. Then, the difference of two frames of images to obtain the target spot. Finally, the appropriate structural element is used to corrode the residual shadow in the image to completely eliminate the adverse effects of stray light. Experimental results show that the recognition accuracy of guided laser spot is better than 93. 75% by using the anti stray light algorithm within the applicable distance of laser target. Compared with the other anti stray light algorithm, the recognition accuracy is improved by 21. 87% , 23. 13% , and 26. 87% , respectively in short, medium and long distance, which can meet the requirements of shield guided construction and has a good application prospect.