Developing multifunctional nanoparticles to support new therapy models is a promising and challenging task to address the current dilemma on antitumor treatment. Herein, we incorporated multifunctional dendritic nanoparticles into a poly(D, L-lactide-co-glycolide)-poly(ethylene glycol)-poly(D, L-lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymers thermosensitive injectable hydrogel matrix to construct a localized drug delivery system for combining chemotherapy and immunotherapy. The multifunctional dendritic nanoparticles were designed with following expectations: i, Dendritic scaffolds provide a hydrophobic interior to load the anticancer drug, doxorubicin (DOX), for chemotherapy; and ii, dendritic scaffolds are used to build arginine-rich molecules to provide the inducible nitric oxide synthase (iNOS) substrate, L-Arg, to M1 macrophages, which can produce the cytotoxic substance nitric oxide (NO) and subsequently induce tumor cell destruction through immunotherapy. It is noteworthy that the dendritic nanoparticles-in-hydrogel delivery system is able to gel at physiological temperature and serves as a warehouse for the sustained release of the drug. Ultimately, this system showed great efficacy in treating 4T1 cells-xenografted BALB/C mice (86.62% tumor growth inhibition). Therefore, this localized drug delivery system combining chemotherapy and immunotherapy provides a novel approach for cancer therapy.