Tumor microenvironment has been widely utilized for advanced drug delivery in recent years, among which hypoxia-responsive drug delivery systems have become the research hotspot. Although hypoxia-responsive micelles or polymersomes have been successfully developed, a type of hypoxia-degradable nanogel has rarely been reported and the advantages of hypoxia-degradable nanogel over other kinds of degradable nanogels in tumor drug delivery remain unclear. Herein, we reported the synthesis of a novel hypoxia-responsive crosslinker and the fabrication of a hypoxia-degradable zwitterionic poly(phosphorylcholine)-based (PMPC) nanogel for tumor drug delivery. The obtained PMPC nanogel showed ultra-long blood circulation and desirable immune compatibility, which leads to high and long-lasting accumulation in tumor tissue. Furthermore, PMPC nanogel could rapidly degrade into oligomers of low molecule weight owing to the degradation of azo bond in hypoxic environment, which leads to the effective release of the loaded drug. Impressively, PMPC nanogel showed superior tumor inhibition effect both and compared to the reduction-responsive phosphorylcholine-based nanogel, owing to the more complete drug release. Overall, the drug-loaded PMPC nanogel exhibits a pronounced tumor inhibition effect in a humanized subcutaneous liver cancer model with negligible side effects, which showed great potential as nanocarrier for advanced tumor drug delivery.