The invention discloses an organic boron crosslinking agent prepared by reacting boric acid with an organic polyamine compound in the absence of water, wherein the organic polyamine compound is selected from diethylenetriamine, triethylenetetramine, 1,4,7,10,13-pentaazatridecane, polyethylene-polyamines or polyethyleneimine. The invention also discloses a guar gum fracturing fluid, which includes,by weight, the following components:0.2%-0.6% of hydroxypropyl guar gum, 0.2%-0.6% of the organic boron crosslinking agent described in claim 1, 0.01%-0.2% of a pH regulating agent, 0-0.5% of a temperature stabilizer, 0.2%-2% of other additives, with the balance being water. The organic boron crosslinking agent of the invention has a large molecular volume and a plurality of cross-linking pointsformed with a low-concentration guar gum aqueous solution, and so, cross-linking properties and temperature resistance performance of a gelled fracturing fluid are improved, the using amount of the cross-linking agent is reduced, and the cost of a fracturing fluid system is reduced. The guar gum fracturing fluid of the invention has good cross-linking properties and good temperature resistance performance, the concentration of the hydroxypropyl guar gum can be adjusted according to the reservoir temperature, and the maximum usage temperature is 150 DEG C.