The precise measurement of the disease parameters is affected by the distance between the underwater camera array and the water-involved parts of structures such as bridges and dams, and the usual image stitching methods depend on the salient feature points. For the above, a method is proposed to measure the object distance and splice the image array based on the image by an underwater camera array and a laser. According to the position of laser spot in the image, the formulas of laser ranging are derived respectively when underwater camera array plane is parallel to the observed surface, when there is a rotation angle and a pitching angle between underwater camera array plane and the observed surface, and the image array is corrected and stitched after the size of the overlapped region is calculated. The experimental results show that the ranging error is less than 2 mm and the relative error is less than 1.5% in the three cases, and correction and stitching of image array are realized well. The method has a great application prospect in underwater disease detection of infrastructure.