Influenza viruses, due to their simple genomic structure and potent immunostimulatory capacity, have been extensively explored for applications in cancer immunotherapy and viral vector vaccine development. However, wild-type influenza viruses possess inherent risks of lethal pathogenicity and transmissibility, which limit their direct application. Special cold-adapted influenza strains have been widely used in live attenuated vaccines, which rely on specific amino acid mutations. With the advancement in synthetic biology and reverse genetics technologies, a variety of next-generation attenuated influenza virus have been developed, including genome-recoded viruses, miRNA-targeted viruses, viruses containing premature termination codons, and proteolysis-targeting recombinant viruses. This study systematically summarized the synthetic biology-based strategies for generating a next-generation method for the attenuated influenza virus, critically discussed the advantages and limitations of each strategy, and further analyzed their applications and challenges in cancer therapy and viral vector vaccine development. By synthesizing current research progress, this review aimed to provide a theoretical basis for constructing safer, more stable, and more controllable influenza virus engineering platforms, and to offer new insights for the design of attenuated influenza virus suitable for tumor therapy and novel vaccine delivery.