The effects of different pipe materials and hydraulic conditions on the formation of trihalomethanes(THMs) were investigated.Pipe section reactor was used for the research of pipe materials and dynamic simulation equipment of water distribution network was used for the research of hydraulic conditions.The results of pipe section reactor showed that the ranking of chlorine decay velocity in different pipe materials was ductile cast iron>PVC>stainless steel,while the ranking of THMs concentration was PVC>ductile cast iron>stainless steel.The results of dynamic simulation showed that a higher flow velocity of water caused higher THMs concentration,but it was not distinct compared with the decay of chlorine.When retention time and flow velocity affected the formation of THMs simultaneously,THMs concentration was dependent on the effect degree of the two factors.THMs concentration increased as pipe diameter was increased.Chlorine residual,pipe materials,flow velocity and retention time are all important effects for the THMs formation.