The invention adopts polyacrylamide and a nano inorganic phase to prepare a polyacrylamide nano composite material through an in-situ polymerization method and then forms a fracturing fluid thickening agent. The nano inorganic phase is prepared by mixing the products of intercalation reactions between an organic long-chain intercalator and layered silicate with magnesium nitrate and aluminum nitrate. The nano inorganic phase, acrylamide monomer, a coupling agent, a complexing agent, an initiator, an oxidant, a reductant, a cosolvent, an auxiliary agent, and deionized water form a suspension fluid reaction system, and the polyacrylamide nano composite material is formed after the polymerization-intercalation composite reactions. The polyacrylamide nano composite material with a mass percentage of 0.25% is taken as the thickening agent, and then is mixed with a crosslinking agent with a mass percentage of 0.20%, a gel breaker with a mass percentage of 0.20%, and other auxiliary agents to form a fracturing fluid system. The system is sheared for 70 minutes under a shearing speed of 170 s<-1> at a temperature of 150 DEG C so as to form a fracturing fluid with a viscosity larger than 50 mPa.s, and the fracturing fluid has the characteristics of high temperature resistance, shearing resistance, low frictional resistance, complete glue breaking effect, and good compatibility with the formation fluid.