According to the problems of that the serious blockage of polymer injection wells, the high injection pressure and the bad effect of polymer injection in Xingnan oilfield, the polymer and water of a block in Xingnan oilfield was adopted to carry out the laboratory experiments on simulation of polymer flooding and plugging and then the reason of blockage was found out.  The results show that the polymer and mechanical impurities are the main factors to cause the pore blockage, and the lower the permeability, the more serious the blockage. Aiming at the blockage reason, laboratory experiment study on the formula of plug removal agent was carried out. Finally the multiple plug removal agent consists of agent A, B and C was determined. On the basis of optimizing the mass fraction of each agent, the injection volume and the injection order, the broken down rate of formations can reach 102.41%~124.77% with this plugging removal agent formula.