Objective To analyze the force condition of a single microparticle in blood vessel and the factors that influencing its motion. Method The microparticles in blood vessel during targeted drug delivery were studied, and the fluid flow in blood vessel was simplified as the Poiseuille flow in parallel plate flow chamber. Specific methods for calculating each force subjected on the single microparticle in the flow field were analyzed. The motion equations of the single microparticle were determined through calculation of its force balance and torque balance. The relationship between the force subjected on the single microparticle and the particle diameter/flow rate as well as the critical motion conditions of the particle diameter and flow rate were obtained by numerical calculation. Results The single microparticle was more subjected to the motion of rolling, sliding and ascending with the increase of flow rate and particle diameter. In flow rate and particle diameter diagrams, the critical curve of ascending motion located above that of sliding motion, while the rolling curve was located at the bottom.Conclusions The microparticle will not do the ascending motion under the condition of blood flow rate in human. As the blood flow rate reduces, the motion of microparticle with given diameter will be transfered from sliding to rolling, and will be entirely still under the condition of elastic deformation. Therefore, the proper selection of mircoparticle diameter and its surface adhesivity is critical for the drug particle to transport to the target location.