Abstract: There are two serious obstacles to tumor immunotherapy. Firstly, the immune response of the tumor is seriously reduced due to immunosuppressive tumor microenvironment (ITM) and low immunogenicity of tumor. The second obstacle is the dense and complex heterogeneous structures, which seriously prevent the nanoparticles (NPs) from penetrating deeper into tumor tissue. Immunogenic cell death (ICD) induced by doxorubicin (DOX) is an effective method to enhance tumor immune activity. However, interferon-γ (IFN-γ) secreted by cytotoxic T lymphocytes (CTL) after ICD induction would increase the expression of indoleamine 2,3-dioxygenase 1 (IDO1) and enhance ITM. IDO1 siRNA would reduce the expression of IDO1 protein, regulate the tumor immunosuppressive microenvironment and regulate ITM, so as to enhance the ICD effect of DOX. In this paper, a novel charge conversional, particle size reduction and highly penetrable NPs based on a pH sensitive copolymer poly(ethylene glycol)-poly-L-lysine-2,3-dimethylmaleic anhydride (mPEG-PLL-DMA, PLD) and polyamidoamine (PAMAM) dendrimers to achieve deep delivery of tumor tissue. DOX and IDO1 siRNA were encapsulated to achieve efficient tumor immunotherapy. Preparation and cell level experiments showed that PLD material had significant pH sensitivity. Results of 3D tumor penetrable experiment in vitro showed that adding the pH sensitive material PLD significantly improved the permeability of the preparation. In addition, 4T1 tumor model was established for BALB/c mice and all animal experiments were displayed in according with the requirements of the Animal Experiment Ethics Committee of Shenyang Pharmaceutical University. The results of in vivo efficacy experiments and tissue experiments evaluated that IDO1 siRNA significantly improved the ICD effect owing to DOX, so as to significantly inhibit tumor growth.