Laboratory research on protective agents for reservoirs was carried out to solve the problem of reservoir damage during drilling in Biyang Sag of Henan Oilfield.Under alkaline conditions,starch microspheres were prepared with corn starch, epichlorohydrin, and polyethylene glycol 20000 as the main raw materials, and then the starch?based protective agent DYB for reservoirs was prepared by the compound of the starch microspheres, regenerated fiber, calcium carbonate (QS?2), and emulsified asphalt (SFT). Scanning electron microscope and thermogravimetric analyzer were used to study the micromorphology and thermal stability of the synthesized product and evaluate the performance of DYB, such as shale rolling recovery and plugging. The results indicate that the particle size of starch microspheres is in the range of 3~5 μm, and the shale recovery rate of DYB in the base slurry is over 85.0%, the API filtration loss of the base slurry after aging at 120~180 ℃ is controlled within 12 mL. After 3.0% DYB is added to the simulated field drilling fluid, its pressure?bearing capacity in the sand bed can reach 4.00 MPa, while the membrane pressure?bearing capacity in the artificial core is over 10.00 MPa, and the recovery value of core permeability is over 82.0%.