A tumor immunotherapy composition based on modified cells, in particular antigen-presenting cells activated by means of attenuated Listeria monocytogenes, a preparation method therefor and an application thereof. Attenuated Listeria monocytogenes carrying a specific antigen plasmid is used to activate antigen-presenting cells, thereby activating MHC antigen presenting properties and a series of cellular immune responses in vivo so as to achieve the purpose of anti-tumor therapy. The described technical solution may specifically activate macrophages and/or dendritic cells, thereby eliciting a series of specific anti-tumor immune responses. The operation process does not require genetic modification of autologous cells, is not limited by tumor type, and operations of the overall process are simple and easy-to-implement. The present invention may activate a series of anti-tumor immune responses in vivo, thereby greatly shortening the treatment process, and significantly improving targeting and safety.