The lack of an effective printable ink preparation method and the usual mechanically weak performance obstruct the functional 3D printing hydrogel exploitation and application. Herein, we propose a gentle pre-cross-linking strategy to enable a loosely cross-linked cellulose network for simultaneously achieving favorable printability and a strong hydrogel network via mediating the cellulose self-assembly. A small amount of epichlorohydrin is applied to (i) slightly pre-cross-link the cellulose chains for forming the percolating network to regulate the rheological properties and (ii) form the loosely cross-linked points to mediate the cellulose chains' self-assembly for achieving superior mechanical properties. The fabrication of the complex 3D structures verifies the design flexibility. The printed cellulose hydrogels exhibit a biomimetic nanofibrous topology, remarkable tensile and compressive strength (5.22 and 11.80 MPa), as well as toughness (1.81 and 2.16 MJ/m3). As a demonstration, a bilayer scaffold (mimicking the osteochondral structure) consisting of a top pristine cellulose and a bottom cellulose/bioactive glass hydrogel is printed and exhibits superior osteochondral defect repair performance, showing a potential in tissue engineering. We anticipate that our loose pre-cross-linking 3D printing ink preparation concept can inspire the development of other polymeric inks and strong 3D printing functional hydrogels, eventually spreading the applications in diverse fields.