With the C# language and Access database, Building Foundation Pit Monitoring Information System (BFPMIS) was developed. At the process of developing the excavation monitoring system, the design of the system data structures and the data types are discussed. The excavation monitoring system contains main data structure and assistant data structure. The data structure, data element and data type of projects, bids, sections, monitoring point types, point property, alert values, bore information, pile information and beam information are analyzed emphatically. The application of the tree structure in the main data structure is introduced. And the monitoring points are classified according to the monitoring objects to describe and store the monitoring data. The system set orange alarm and red alarm to every monitoring point.