ObjectiveTo survey the retraction of  dental unit waterlines (DUWLs) in medical institutions, and evaluate the influencing factors for retraction of DUWLs.MethodsIn MayNovember 2014, dental chair units(DCUs) in medical institutions in Tianjin City were sampled through systematic random sampling method, retraction volume of DUWLs was detected by independently made detector, the relevant influencing factors were  investigated.ResultsA total of 58 DCUs in 30 medical institutions in 10 districts(counties) of Tianjin  were investigated,the average retraction volume of DUWLs was （103.60±117.85 ）mm3, the qualified rate of retraction volume of DUWLs was 48.28 %（28/58）；length of utilization of DCUs was positively correlated with DUWLs  retraction （r=0.52，P＜0.001）.There were no significant difference in retraction volume of DUWLs among medical institutions in different districts(counties), levels of  medical institutions,DUC brands, and modes of DUC water supply(all P＞0.05).ConclusionThe qualified rate of retraction volume of DUWLs is low, routine maintenance of DUCs needs to be intensified,especially the longterm used DUCs,  contaminatin of DUWLs due to the invalidity of retraction valve should be prevented.