Abstract： Objective To evaluate the value of pre-S1 Ag in combined detection of hepatitis B virus. Methods 288 patients' serums with chronicity type B hepatitis (CHB)were collected when they had been detected with HBV-DNA,HBVM or ALT/AST,and then ELISA assay were applied to detect pre-S1Ag. Results A total of 288 patients ,including 175 males and 113 females( their meso-age is 36.89 years old) were recruited into this study. 161 patients were pre-S1 Ag positive(68.4%), 197 patients' HBV DNA contents exceeded 5.0E + 2 copy/ml(55.9%) ,71patients were H BeAg positive (24.6%), 186 patients were HBeAg negative (64.58%). The rate of 64 patients' ALT and AST exceeded 0. 84, and their' ALT exceeded 40 u/ml ( 22. 2% ). 60 patients' AST exceeded 50 u/ml (20. 8% ). These patients were divided into pre-S1 Ag positive group and pre-S1 Ag group. In pre-S1 Ag positive group, 124 patients' HBV DNA contents exceeded 5.0E + 2 copy/ml( 62.9% ), 118 patients were HBeAg negative (59.8%). When HBV DNA content was less than 5.0E+2 copy/ml,pre-S1 Ag positive rate was 35.2% and pre-S1 Ag negative rate was 63.6%. when HBV DNA content was less than 5.0E + 3 copy/ml, pre-S1 Ag positive rate was 56.9% and pre-S1 Ag negative rate was 81.7%. When HBV DNA content exceeded 5.0E + 5 copy/ml but less than 5.0E + 8 copy/ml ,pre-S1 Ag positive rate was 33% and pre-S1 Ag negative rate was 14.3% ,so two groups had significant difference. Conclusion Pre-S1 Ag positive and HBeAg negative in the CHB patients serums signify virus replication,and it can help us decide prognosis.