Swine influenza virus (SIV) is a highly contagious respiratory pathogen in pigs, with bidirectional transmission posing a potential threat to human health. In this study, nasal swab samples were collected from pigs in Shandong Province, China, and yielded an H1N2 SIV strain, designated A/swine/Shandong/QD726/2021 (H1N2). Whole-genome sequencing was performed for Sw/SD/QD726/2021, and phylogenetic analysis was conducted together with 156 Chinese H1N2 reference sequences obtained from the Global Initiative on Sharing All Influenza Data (GISAID) database and the National Center for Biotechnology Information (NCBI) Influenza Virus Resource database. The results indicated that Sw/QD726/2021 represents a novel reassortant genotype (G21), with the HA gene derived from Eurasian avian-like H1N1 (EA H1N1), the NA and NS genes from triple-reassortant H1N2 (TR H1N2), and the remaining internal genes (PB2, PB1, PA, NP, M) from the 2009 pandemic H1N1 (pdm/09 H1N1). Key amino acid analysis revealed N31 in M2, responsible for adamantane resistance, and S42 in NS1, which influences viral virulence in mouse models. BALB/c mouse experiments demonstrated efficient viral replication in the lungs and nasal turbinates, accompanied by moderate body weight loss and lung lesions, indicating only moderate pathogenicity. These findings underscore the ongoing evolution of H1N2 SIV in pigs and emphasize the importance of enhanced surveillance and preventive strategies to mitigate public health risks.