Abstract: Conventional guar fracturing fluid will damage core permeability after gel?breaking, and influence oil well productivity after fracturing stimulation. Based on the analysis on guar fracturing fluid compositions, dynamic and static adsorption experiments and core?damage experiment are carried out for artificial cores and natural cores. Artificial core?damage experiment result shows that the damage of guar breaking liquid can be classified as water damage and guar retention damage, of which water damage is more serious than guar retention damage. Adsorption experiment result shows that the retention of the guar molecules of gel?breaking liquid in pores of cores can be classified into adsorption and trapping, accounting for 43.6% and 56.4% in average, respectively. The result from natural core damage experiment in Yuanba area also shows that the gel?breaking liquid in guar fracturing fluid has an aqueous?phase damage to natural cores. Guar molecules after gel?breaking have less impact on permeability of natural cores compared with aqueous?phase damage