This article proposes that the boundary problem of the express delivery corporations is evitable by comparing the express delivery corporations in China with UPS, FedEx, DHL, and TNT. There are limitations in explaining the boundary of express delivery corporations. Based on the concept of transaction cost theory, this paper tries to explain the boundary of the express delivery corporations by combining with the spatial-temporal characteristics of express delivery. The results show that vertical integration and unlimited expansion in space of the network are the two characteristics of the express delivery corporation boundary. By analyzing the scale evolution of the Chinese express delivery, the above results are proved and the expansion of the express delivery scale is proposed.