Connection the upper components and disconnection the other components is widely used in the expressway hollow slab bridge widening and reconstruction. How to design the transverse joint between newly-built and existing bridges is a key problem in the renovation of prestressed concrete bridges. In this paper, combined with a freeway widening project, 2 kinds of different connection forms were compared by their transverse distribution influence lines, which were calculated by finite element method. The results show that the new and old bridges are working together after widening, which makes vehicle loads of the slabs of the old bridge are reduced, especially the side slab of old bride which was next to the slab of newly-built bridge dropped by nearly 50%. So the bridge widening strengthens the safety of old bridge. And the weak connection of the bridge is always the connection of newly-built bridge and existing bridge, which is accorded with practical situation. So the particular attention should be given to the connection. It provides a basis for widening the old bridge and a reference for widening and maintenance the same kind of bridges.