The roles of shear rate, shear time, red blood cell (RBC) concentration and RBC rigidity in the spontaneous platelet aggregation of whole blood at uniform flow field were studied. A new rigid RBC model was established by heating and assessed by studies of hemorheology, RBC electrophoresis, and RBC aggregation. In uniform flow field formed with cone-plate viscometer, both of the effect of shear rate and shear time on the spontaneous platelet aggregation rate (SPAR) were appeared in the bidirectional patterns. At low shear rate, SPAR increased with the prolongation of shear time, but at hight shear rate the time prolongation decreaed SPAR. Similiarly, SPAR was positively related to the shear rate at early shearing, with the increasing of shear time, the relationship of SPAR with shear rate changed from positive to negtive. When the shear rate at 46 s~(-1) or the shear time at 20 minutes, SPAR was unaffected by shear time or shear rate, respectively. With increase of RBC concentration, SPAR increased correspondingly (r=0.8235, P