48 eligible healthy subjects are involved. According to the set ascending-doses groups, subjects will be randomized in a 3:1 proportion to orally take a single dose of Metacavir enteric-coated capsule or placebo on the condition of fasting. Each group has 8 people, evenly composed of men and women. The beginning dose of the study is 40mg/d.According to the dose escalation method, subjects who have successfully completed tests of the previous dose group and passed the safety assessment will enter the next dose group with the same method. All subjects check in the phaseⅠresearch center one day early before taking the test drug. Vital signs and ECG will be observed before and 0.5,1,2,4,8,12,18,24,48,72 hours after administration and at the follow-up day which is the 7th day since administration. Laboratory tests will be conducted before and 6,24,48,72 hours after administration and at the follow-up day , and the adverse drug events are observed throughout the test.