In recent years, vitamin D (VD) has received much attention in the fields of host immune regulation, inflammation, fibrosis, cell proliferation and differentiation and tumor. VD works by binding to the vitamin D receptor (VDR). VDR is mainly distributed in giant cells, dendritic cells, T cells and lymphocytes. Four SNPs of VDRS have been most studied: TaqI (rs731236), FokI (rs10735810), ApaI (rs7975232), and BsmI (rs1544410). At present, more and more patients have been treated with oral nucleotide/nucleoside analogues (NAs) with direct antiviral drugs in China, and a large part of them show low expression of HBsAg. Clinical cure can be pursued for these patients, that is, HBsAg turns negative. A number of studies have been carried out at home and abroad.

In this study, We will recruit CHB patients with low HBsAg levels. They all will receive pegylated interferon treatment and were randomly assigned to a vitamin D treatment or a control group. A final assessment will be made to determine whether vitamin D levels would affect the clearance rate of HBsAg.

Inclusion Criteria:

1.According with the diagnosis of chronic hepatitis B in the guideline of China in 2015 2.18-60 years old 3.More than 1 year history of nucleot(s)ide analogues therapy with HBsAg ≤1500 IU/ml, negative HBeAg and HBV DNA<100 IU/ml 4.No contraindications of interferon

Exclusion Criteria:

1. Allergy to interferon
2. Alanine transaminase >10 times of upper limit of normal(ULN) or total bilirubin >2 times of ULN
3. existing or previous decompensated liver cirrhosis
4. White blood cells or Platelet below the lower limit of normal
5. existing severe organ injury
6. combined with autoimmune diseases, psychiatric diseases, diabetes or thyroidism
7. confirmed or suspected malignant tumors
8. before or after transplantation
9. using immunosuppressor
10. pregnant or having a planned parenthood in 2 years
11. alcohol or drug addicted
12. infected by HIV
13. any conditions that is unsuitable to interferon therapy according to the doctors' judgement