On web crack,one of the major problems existing in pre- stressed concrete continuous box- beam bridges,few studies have been conducted.In this paper,according to the monitoring results of a continuous box- beam bridge with constant cross- section,the major tensile stresses in the web with different thickness were discussed withthe finite element software ANSYS,and the causes of cracks were analyzed.Moreover,some reinforcement mea-sures such as employing steel plate and sealing epoxy resin were taken,and the reinforcement effect was finally con-firmed by observations. The results show that the crack is greatly related to the web thickness and the web steel,so that the web thickness should be larger than 60cm; and that,after the reinforcement,there is no crack propagation and appearance in width and length directions,which means that the proposed reinforcement measures can effec-tively control further development of diagonal cracks of web and possess high feasibility and effectiveness.