Based on the characteristics of fluids suffering high shear stress caused by large pumping rate in slick water fracturing of shale gas reservoir, evaluation of four kinds of anionic drag reducer is carried out in laboratory at high shear rates utilizing large friction tester. The results show that, the drag reducer XT-65B has a better drag reduction efficiency, which can be up to 56%. Meanwhile, the factors affect the drag reduction efficiency, such as shear rates, shearing time and shearing path, are analyzed as well. With the increase of shear rate, resistance reduction rate of drag reducers is on the decline. At low shear rete conditions (500 s-1), the resistance reduction rate of drag reducers is not sensitive to the shear time; at the high shear rate conditions (5 000 s-1), the resistance reduction rate of drag reducers cut sharply with the increment of shearing time. Different shear paths affect the performance of drag reducers significantly,high shear rate can exert an unrecoverable damage on the molecular structure of drag reducer. The micro-structure of drag reducer molecule of XT-65B before and after shearing is also observed with the help of SEM, confirming that the drag reducer molecule is little affected at low shear rates（500 s-1）and degrades greatly at high shear rates（5 000 s-1）,which has a good agreement with the experimental results.