Substantial progress has been made with cancer immunotherapeutic strategies in recent years, most of which mainly rely on enhancing the T cell response. However, sufficient tumor antigen information often cannot be presented to T cells, resulting in a failed effector T cell response. The innate immune system can effectively recognize tumor antigens and then initiate an adaptive immune response. Here, we developed a spontaneous multifunctional hydrogel (NOCC-CpG/OX-M, Ncom Gel) vaccine to amplify the innate immune response and harness innate immunity to launch and maintain a powerful adaptive immune response. Ncom Gel was formed by a Schiff base reaction between CpG-modified carboxymethyl chitosan (NOCC-CpG) and partially oxidized mannan (OX-M). The effects of the Ncom Gel vaccine on DCs and macrophages and antigen-specific humoral immunity and cellular immunity were studied. Furthermore, the antitumor immune response of the Ncom Gel vaccine and its effect on the tumor microenvironment were evaluated. The Ncom Gel vaccine enhanced antigen presentation to T cells by facilitating DC uptake and maturation and inducing macrophages to a proinflammatory subtype, further leading to a T cell-mediated adaptive immune response. Moreover, the innate immune response could be amplified via the promotion of antigen-specific antibody production. The Ncom Gel vaccine reversed the tumor immune microenvironment to an inflamed phenotype and showed a significant antitumor response in a melanoma model. Our research implies the potential application of injectable hydrogels as a platform for tumor immunotherapy. The strategy also opens up a new avenue for multilayered cancer immunotherapy.