In this work, to obtain a novel composite hydrogel with high mechanical strength, fluorescence and degradable behavior for bone tissue engineering, we prepare a nanofiller and double-network (DN) structure co-enhanced carbon dots/hydroxyapatite/poly (vinyl alcohol) (CDs/HA/PVA) DN hydrogel. The composite hydrogels are fabricated by a combination of two fabrication techniques including chemical copolymerization and freezing‒thawing cycles, and further characterized by FTIR, XRD, etc. Additional investigations focus on the mechanical properties of the hydrogel with varying mass ratios of CDs to PVA, HA to PVA and different numbers of freezing/thawing cycles. The results show that the as-prepared CDs/HA/PVA DN hydrogel has optimized compression properties (Compression strength = 3.462 MPa, Young's modulus = 4.5 kPa). This is mainly caused by the synergism effect of the nanofiller and chemical and physical co-crosslinking. The water content and swelling ratio of the CDs/HA/PVA SN and DN gels are also systematically investigated to reveal the relationship of their microstructural features and mechanical behavior. In addition, in vitro degradation tests of the CDs/HA/PVA DN hydrogel show that the DN hydrogels have a prominent degradable behavior. So, they have potential to be used as high-strength, self-tracing bone substitutes in the biomedical engineering field.