A study was conducted to address the issue of insufficient injection caused by pressure increase after injection of polymer microspheres into oil and gas field injection wells. By studying the effects of factors such as the dosage of the plugging agent， temperature and time on the viscosity and particle size of the microsphere solution，the working conditions of the plugging agent were optimized. At the same time，the field test was carried out. The results showed that the unblocking agent，composed of 30%JT-1+35% HRJ+22% APG0814+10% H₂O+3% NaCl，could significantly reduce the particle size and viscosity of the microspheres. At the same concentration of unblocking agent，the longer the unblocking time，the better the unblocking effect，and the suitable unblocking time is greater than or equal to 4 hours. The higher the reaction temperature，the better the blockage removal effect. At the same salt concentration，the order of influence on the effectiveness of the unblocking agent was obtained as follows：NaCl≥ KCl＞NH₄Cl. At room temperature，adding 5% unblocking agent into 2% microsphere solution，the viscosity of the microsphere solution was 1.46 mPa s，and the average particle size of the microsphere was 204.6 nm after reaction for 4 hours，compared with the blank sample without the unblocking agent，the viscosity being of 2.17 mPa s and average particle size being of 3243.74 nm，the viscosity of the unblocking solution decreased by 33%，and the particle size decreased by nearly 94%. The solid content in the unblocking residue decreased from 675 mg/L to 70 mg/L，the decrease being of nearly 90%. The surface tension of the residue was 24.89 mN/m，and the interfacial tension was 1.849×10^-2 mN/m，possessing the high surfacial/interfacial activites. The unblocking agent was tested on-site in Changqing and achieved good results in reducing pressure and increasing injection.