The invention discloses temperature-resisting salt-tolerant high-temperature self-cross-linking onsite polymerization water plugging gel which mainly consists of, by mass, main agent 4%-6%, cross-linking agent 1%-2% and the balance saline water. The main agent consists of a monomer A and a monomer B, wherein the monomer A is acrylamide, and the monomer B is ester matter. The cross-linking agent is one of or a mixture of two or more formaldehyde, phenolic resin, resorcinol, hexamethylene tetramine, paraformaldehyde and polyethyleneimine. The temperature-resisting salt-tolerant high-temperature self-cross-linking onsite polymerization water plugging gel spontaneously produces cross-linking polymerization under the condition of high temperature, an initiator is not added, the gelling time can be controlled to be 2 hours to 28 hours at the temperature of 120 DEG C, the water plugging gel can be directly prepared by high-salinity water, the gelling strength can be up to the visual inspection code level I, and synaeresis does not occur after 90 days. The temperature-resisting salt-tolerant high-temperature self-cross-linking onsite polymerization water plugging gel is low in initial viscosity, has the advantages of being few in components, good in instant solubility and pumping injection performance, high plugging strength, good in thermohaline stability, low in cost and the like and has wide application prospect on the aspect of high-temperature high-salinity oil reservoir profile control water plugging.