Urban viaducts provides fast passage for commuting in modern cities. Precast small-box beam bridges have the advantages, such as low cost, wide range of application, high construction quality and short erection time. Hidden bent cap can supply more clearance under the viaduct in contrast to exposed bent cap. Taking a viaduct built in Ningbo City as an example, the two bridge systems are modeled with ABAQUS finite element software to study the stress, deflection and transverse distribution characteristics of box beams. And the transverse distribution is calculated theoretically. The results show that the box beam stress of hidden bent cap scheme is smaller than that of exposed bent cap scheme, but the live load deflection of hidden bent cap scheme is larger than that of exposed bent cap scheme. The transverse distribution coefficient of side beam with hidden bent cap is larger than that of the side beam with exposed bent cap, both of which are larger than the theoretical values. The transverse distribution coefficient of middle beam with hidden bent cap is nearly the same with that of the middle beam with exposed bent cap, which is close to the theoretical value.