Recently, digital light processing (DLP) 3D printing has garnered significant interest for fabricating high-fidelity hydrogels. However, the intrinsic weak and loose network of hydrogels, coupled with uncontrollable light projection, leads to low printing resolution and restricts their broader applications. Herein, we propose a straightforward DLP 3D printing strategy utilizing in situ phase separation to produce high-fidelity, high-modulus, and biocompatible hydrogels. By selecting acrylamide monomers with poor compatibility within a polyvinyl pyrrolidone (PVP) network during polymerization, we create phase-separated domains within polyacrylamide (PAM) that effectively inhibit ultraviolet (UV) light transmission. This regulation of UV light distribution results in anhydrous inks with exceptional properties: ultra-high resolution (1.5 μm), ultra-high modulus (1043 MPa), and high strength (70.0 MPa). Upon hydration, the modulus and strength of the hydrogels decrease to approximately 4000 times those of the anhydrous gels, exhibiting high mechano-moisture sensitivity suitable for actuator applications. Additionally, the DLP 3D-printed hydrogels, featuring micro-scale structures, demonstrate good biocompatibility and facilitate nutrient transport for cell proliferation. This versatile DLP 3D printing strategy paves the way for the fabrication of high-fidelity and multifunctional hydrogels.