 In order to optimize HBsAg clearance in CHB patients with low level HBsAg, the investigators enrolled patients who had received, and responded to, NAs for more than 12 monthssee the inclusion criteria, and patients are switched to receive peginterferon alfa-2a 180 microgramsweek or peginterferon alfa-2b 80 microgramsweek. The longest course of treatment is 96 weeks. After treatment, patients will be followed up for 24 weeks. During the 96 weeks course of treatment, HBsAg level will be monitored. When HBsAg level is less than 0.05 IUmL, peginterferon treatment will be stopped and patients will receive 24 weeks follow up. 