The invention discloses a preparation method of photo-crosslinking polyvinyl alcohol/nanocrystalline cellulose PVA/CNC compound hydrogel and belongs to the macromolecular material field and the photosensitive material field. The preparation method includes: adding natural polymer CNC into a PVA solution to obtain a PVA/CNC mixed solution; adding N,N'-methylenebisacrylamide (MBA) containing a carbon-carbon double bond and an amino group into the mixed solution to allow the MBA to have hydrogen-bond interaction with the PVA and CNC, performing polymerization under the ultraviolet irradiation at the same time, and performing circulating freezing-unfreezing treatment to obtain the photo-crosslinking PVA/CNC compound hydrogel. The photo-crosslinking PVA/CNC compound hydrogel is capable of improving the mechanical property of PVA hydrogel and allows the PVA hydrogel to be well applied in various fields such as agriculture and gardening, biological medicine and environment protection.