Buildings　are　one　of　the　typical　underlying　surfaces　of　cities,　but　the　study　of　hydrological　effects　of　buildings　is　a　weak　link　in　urban　hydrological　research.　Indoor　temperature　and　humidity　are　important　embodiments　of　the　hydrological　effect　of　building　water　activity.　Beijing,　as　the　capital　of　China,　is　selected　as　the　representative　research　area　in　north　China.　The　variation　characteristics　of　temperature　and　humidity　of　residential　buildings,　as　well　astheir　relationship　with　each　other,　are　analyzed　through　experimental　monitoring.　The　result　showsthat　human　water　use　activities　in　buildings　will　increase　indoor　humidity.　The　indoor　humidity　is　higher　than　the　outdoor　humidity　in　the　sunny　days　of　spring,　summer　andwinter,　while　it　is　lower　than　the　outdoor　humidity　through　rainy　days　and　the　whole　autumn.　Both　indoor　and　outdoor　humidityreach　peak　and　nearly　the　same　at　night,　but　the　difference　between　the　indoor　and　outdoor　humidity　is　obvious　during　the　daytime.　Based　on　the　results　we　can　draw　the　conclusion　that　(1)　indoor　water　use　activities　canproduce　obvious　water　vapor　diffusion;　(2)　In　northern　China,　the　indoor　humidity　of　the　residential　buildings　is　higher　than　the　outdoor　humidity,　and　will　flow　to　outdoors　during　most　sunny　days;　(3)　among　all　the　types　of　the　rooms　in　the　resendital　building,　bathroom　is　the　largest　contributor　to　water　vapor　dissipation.　We　suggest　that　water　vapor　dissipation　in　buildings　should　be　taken　into　account　in　the　study　of　evaporation　in　urban　areas　since　it　may　profoundly　affect　the　urban　hydrological　cycle.　©　Published　under　licence　by　IOP　Publishing　Ltd.