To enhance the affinity of the human epidermal growth receptor 2 (HER2) targeted peptide developed previously, bispecific fusion peptides P1GCGT1 and P1GCGCGT1 were designed using an in silico approach. Molecular dynamic simulation showed that both peptides strongly interacted with HER2 domains II and IV. Compared with peptides targeting each single domain, P1GCGT1 and P1GCGCGT1 could bind to HER2 more significantly and targeted HER2-positive cells specifically. Additionally, both peptides were used to generate peptide-drug conjugates with camptothecin (CPT), among which I-1 and I-4 were screened for enhanced cellular activity and selectivity. Biological evaluation demonstrated that I-1 and I-4 induced cell apoptosis, promoted cell cycle arrestin S-phase, and inhibited Topo I activity. The binding affinity assay and confocal analysis revealed that I-1 and I-4 were effective at targeting HER2. Moreover, I-1 and I-4 showed better stability than single targeting peptide and presented enhanced antitumor activity and safety than CPT in tumor-bearing mice.