Abstract: Objective: To observe the effect of profound hemodilution on prat of blood elements and hemodynamics and to supply theory base for clinical proper infusion. Methods: 20 patients undergoing elective operation received hemodilution which was accomplished by infusion of Ringer Ⅱ and 6% hydroxyethyl starch at the rate of 20 ml·kg^-1·h^-1 respectively during the first hour of the operation.Then infusion rate was adjusted according to bleeding and urine output.Hemanalysis, Serum osmolarity, CVP,MAP,HR,Sp0₂ and urine output are all measured at different time of preinfusion,ten minutes after postinfusion and postop-eration. Results: Hct.lowered by 0.27 10min after postinfusion.Plt.RBCG and MCHC decreased by 0.24 percent, 0.0025 cell/L and 5.75g/L respectively（P＜0.05）.CVP returned to 1.23 kPa from origional 0.27 kPa（P＜0.05）.Serum osmolarity had no significant change （P＞0.05）.MAP.HR and Sp0₂ were stable.Urineoutput was 35 ml.10min after postinfusion and 510ml after postoperation.All measured data of postoperation exept Urineoutput were the same as those of lOmin after postinfusion. Conclusions: infusion at the rate of 40 ml ·kg^-1·h^-1 during the first hour of the operation belongs to mild-medius hemodilution which helps to sustain smooth circulation and diminish blood loss and complications.