The PLA grafted NVP copolymer microspheres were prepared by solvent evaporation extraction method using nimodipine as the model drug and analyzing main factors such as the PLA concentration, the emulsifier concentration, stirring speed and dosing ratio with orthogonal design. The surface morphology of the microspheres was scanned under electron microscope and formulation of microspheres was confirmed by FTIR. Characteristics of the powder partical such as mean diameter, drug loading rate and entrapment rate were evaluated comprehensively, and its in vitro release properties were studied. The results showed the copolymer microspheres were round and the surface was smooth, the average particle size were less than 10μm with narrow particle size distribution, with preparation process of 4% PLA concentration, 3% emulsifier concentration, 9000r/min stirring speed and 2/3 dosing ratio. The microspheres release of more than 14 days, and the release rate increased with the increasing graft ratio.