Abstract: Hydrautic factors in designing and operating of constructed wetlands are analysed, with the Bainikeng constructed wetland system as a case study. It is indicated that the Ergun's equation is more appropriate than the Darcy's law to describe the flow in gravel media. A digital solution to Eugun's equation is presented and a tentative designing procedure for constructed wetlands is suggested from the consideration of hydrautic factors, which is helpful in practice.Key word Cons-tructed wetlands; Wastewater treatment; Infiltration hydrau-tics.