Wireless sensor network (WSN) based structural health monitoring (SHM) system attracts increasing interest in recent years. However, the restricted bandwidth, memory and energy pose great challenges to the application of SHM in large scale building. Supported by a real engineering project, a WSN based prototype of SHM system is designed in this paper. Acceleration data, synchronously sampled in each sensor node, are transported to a data processing computer through a base station. In order to achieve a high network throughput, a time division multiple access (TDMA) approach is proposed to reduce the packet collision and energy consumption. 17 sensor nodes, one base station and a processing computer are distributed to validate the prototype system. Test results present that the approach, we proposed, can reduce the signal collision and increase data throughput. The prototype is feasible to the SHM project of a large scale building.