Objective To explore the ideal speed for the infusion of loading dose of dexmedetomidine in patients with hypertension.Methods One hundred and twenty patients with essential hypertension were selected,and they were randomly divided into A,B,C,D four groups according to the digital table,30 cases in each group.All patients were administered the same loading dose(1.0μg/kg) of dexmedetomidine according to the total body weight,the pump infusion time in the four groups was 10,15,20 or 25min,respectively.The mean arterial pressure (MAP) and heart rate(HR) were observed before infusion(T0) and 5 min (T1),10 min (T2),15 min (T3),20 min (T4),25 min(T5),30 min(T6),35 min(T7) after administration.Results Compared with before injection,A group had an increase of MAP[(116.0± 3.4)mmHg] at the point of T3 (t =17.32,P =0.001),B group had an increase of MAP [(115.0 ± 3.3) mmHg] at the point of T3 (t =16.21,P =0.003),C group and D group had no increase of MAP at the point of T0 ～ T7.Conclusion Loading dose (t.0 μ.g/kg) of dexmedetomidine should be pumped in more than 20 min in patients with primary hypertension to maintain steady blood pressure.