The invention discloses a polyhydroxy thickener and a high-temperature-resistant alcohol-based fracturing fluid system. The polyhydroxy thickening agent is formed by copolymerizing three monomers, namely acrylamide, N-vinylpyrrolidone and N-acrylamide propyl-N,N,N-dimethyl hydroxyethyl ammonium chloride, in an aqueous solution; and based on the total mass of the monomers, the mass ratios of acrylamide, N-vinylpyrrolidone and N-acrylamide propyl-N,N,N-dimethyl hydroxyethyl ammonium chloride are 40-85%, 5-35% and 3-25%, respectively. The high-temperature-resistant alcohol-based fracturing fluidsystem is prepared from the following raw materials: the polyhydroxy thickener, a composite cross-linking agent, a regulator, high-flash-point alcohol and water. According to the alcohol-based fracturing fluid system disclosed by the invention, the polyhydroxy thickening agent is introduced, so the alcohol-based fracturing fluid system has relatively high temperature resistance and shearing resistance, and can resist a temperature of 160 DEG C or above; by using the high-flash-point alcohol, the fracturing system is safer; and an alcohol/water ratio can be increased to 60% or above, even an anhydrous system with the alcohol/water ratio of 100% can be realized, so the fracturing fluid system has the advantages of high flowback rate, small stratum damage, safety, environment friendliness andthe like.