The invention relates to the field of oil and gas exploration and production plugging, in particular to a modified cellulose crosslinking copolymer and gel and a composition and an application thereof. The modified cellulose crosslinkingcopolymer is composed of a crosslinking structure center and a graft polymerization chain grafted on the center of the crosslinking structure, wherein the center of the crosslinking structure is provided by a phenolic resin, The graft polymerization chain is provided by the modified cellulose and the content of graft polymerization chain in the crosslinking copolymer is 50-90 weight %. The gel is prepared by controling gelation time under certain conditions by using the composition, thereby forming a gel containing the modified cellulose crosslinking copolymer. The gel is characterized by high strength, high adhesion, high resistance to salt and salinity, which is beneficial to oil and gas exploration and production.