The rainwater utilization possesses multiple functions as water sources exploration, flood detention, flood storage, and environment beautification. Since there is a great need of water for toilet-flushing, irrigation of gardening campus, and the rainwater collecting area on campus is large, so it can be identified as the exemplary zone for rainwater utilization. This research imitated the daily water balance method by using MATLAB programming and based on the daily rainfall data records in a primary school of Hefei. The reasonable reservoir volume, rate of rainwater utilization and tap water substitution were determined from the perspectives of water balance, economical efficiency, the scale and benefit of campus rainwater utilization. With the ever increasing scarcity of water resources and the water pollution, rainwater utilization in school campus has a great water saving significance and developing prospect of development.