Based on the anti-HBV infection therapy clinical data of the Peginterferon Alfa-2a plus placebo for HBeAg-Positive chronic hepatitis B patients, this paper establishes a mathematical model consisting of three differential equation systems and aims to describe and understand the dynamics of host cells, viruses, the immune system, as well as predict the long term curative effects. The results of numerical simulations indicate that patients whose plasma HBV DNA levels equal the mean HBV DNA levels of all patients will need to prolong their treatment time to 19 years in order to completely eliminate the HBV virus in infected hepatocytes.