As one of the key features of the immune active (IA) phase (HBeAg-positive) in chronic hepatitis B (CHB), liver fibrosis (LF) is a critical treatable stage to avoid progressing to hepatocellular carcinoma (HCC). There is an urgent need to establish mouse models that mimic CHB during this phase to clarify the mechanisms underlying hepatitis B virus (HBV) clearance and liver injury, as well as to facilitate therapy development. In the present work, we introduce a novel HBV mouse model via injections of porcine serum (PS, an immunological liver injury inducer), in combination with hydrodynamic injection of pAAV-HBV1.2 plasmid. The (pAAV-HBV1.2+PS BALB/c) mouse model we developed exhibits the typical features of the IA phase in CHB, including high/intermediate serum HBsAg levels, positive HBeAg and HBV DNA, intermittent elevation of serum alanine aminotransferase, and significant LF. Notably, despite dramatic increases in both duration and intensity of HBV viremia, PS induced definitive LF within 12 weeks only in BALB/c, not in C57BL/6J mice. The heightened functional adaptive immunity impairment, characterized by increased PD-1/PD-L1 signaling, may contribute to the improvement in HBV persistence, whereas intermittent HBV activation, followed by liver injury induced by PS injection, primarily drives LF progression. Furthermore, we validate the characteristics of this model by treating the model with entecavir (an HBV replication blocker). Consequently, we have established a novel CHB mouse model in the IA phase, which undoubtedly holds significant value for deepening our understanding of CHB progression mechanisms and evaluating corresponding therapies.IMPORTANCEHere, we constructed a novel mouse model which shows the typical features of IA phase chronic hepatitis B, including positive serum HBV-indicators (hepatitis B surface antigen, HBsAg; hepatitis B e antigen, HBeAg and HBV DNA), intermittent serum alanine aminotransferase elevation, and significant LF. This model could be a valuable platform for understanding the mechanisms associated with virus clearance, liver damage, immune tolerance, and immune activation, and for the development of therapies. The PS injections can remarkably attenuate the clearance of HBV in pAAV-HBV1.2 mice (BALB/c and C57BL/6J), but only in HBV carrier BALB/c mice induce moderate/severe LF. Impairment of adaptive immunity by PS injections accounts for the model's HBV-persistence improvement, whereas the intermittent HBV activation and immunological liver injury by each PS injection in pAAV-HBV1.2 mice are responsible for LF. Blockage of HBV replication can diminish LF progression. These findings provide new insights into the study of interactions between immune responses and the virus.