During the initial period of precast prestressed concrete box girders in a bridge, some cracks appeared in five box girders. The paper describes the crack states including location, elongation, space, width and depth. The geneses of the cracks are analyzed considering the concrete proportion, environmental condition and construction procedure. Four of them were permitted to be used after mending of these cracks and another one was abandoned directly. After the preventing measurement was adopted, no cracks appeared in the follow-up precast box girders. The experience can be as reference for the similar construction works.