The invention relates to a double-layer highway bridge with integrated upper beam on a frame mound and diaphragm of polycarbonate (PC) continuous box girders. Two layers of PC continuous box girders are arranged on the frame mound of the double-layer highway bridge, an upper-layer base and a lower-layer base are arranged on the frame mound of the double-layer highway bridge, and an upper-layer PC continuous box girder on the upper-layer base is integrated with the beam on top of the frame mound. The double-layer highway bridge omits the beam on top of the frame mound, and the beam on top of the frame mound is integrated with the diaphragm of PC concrete box girders. A structure in which the diaphragm of the upper-layer PC continuous box girders is integrated with the beam on top of the frame mound is a prestressed reinforced concrete structure, the length of the structure is equal to the width of a frame mound cross bridge, and the structure runs through the whole bridge width transversely. The double-layer highway bridge greatly reduces the overall building height of a bridge, reduces self-weight, reduces stress on the lower-portion structure, and improves distortion effect of the PC continuous box girders. Sight lines of driving staff on a lower-layer bridge surface are wide and comfortable, and the double-layer highway bridge can be constructed independently and is low in construction cost.