A large naïve phage displayed human single-chain variable fragments antibody (scFv) library and an in vitro immune library were constructed in parallel conditions, based on the PBLs from healthy and sero-negative blood donors, part of which were in vitro immunized by peptide PreS1 conjugated to BSA. After 3 rounds of panning against PreS1, measurement of antibody-antigen reaction revealed: a scFv specific to PreS1 from the immune library was obtained, which affinity (k=10^-7～10^-8 M) was higher than that from the naïve one (k=10^-6～10^-7 M). Sequencing of the two scFv showed they were human antibodies, which may be of interest in therapy of Hepatitis B. This investigation also illustrated that the method of in vitro immunization results in antibody library more satisfied even than the large naïve one.