This invention provides preparations and applications of a highly strong and tough photo-crosslinked hydrogel material. The hydrogel materials are made from the o-nitrobenzyl phototriggers modified photosensitive polymer derivative, double bond groups modified polymer derivative, and photoinitiator. This invention significantly improved the properties of hydrogels by controlling the average molecular weight (arm length) of photosensitive poly (ethylene glycol) (with o-nitrobenzyl phototriggers modification) and its derivatives, and the molar ratio of o-nitrobenzyl phototriggers to poly (ethylene glycol) and its derivatives. Compared with prior technologies, the strength and/or toughness of the hydrogels in this invention are increased by one order of magnitude or even higher. These advances solve the problems of weak mechanical properties in current hydrogel materials and widen the applications of hydrogel materials.