Platelet aggregation, a vital phenomenon which occurs hundreds of times daily in blood vessels, is the main cause of closing minute ruptures. This paper seeks to simulate platelet aggregation with a unique particle base method as to monitor the impact of blood velocity during thrombi formation. Related literatures applied various computational methods and determined that the rate of growth of aggregated platelet depends markedly on blood flow velocity.Dissipative Particle Dynamics (DPD) method is potentially effective in simulating mesoscale hydrodynamics. This is an advantageous idea behind this method which enables it to run with lower computational cost in comparison with other methods such as Molecular Dynamics (MD). Therefore, in this work we investigate the dependence of the adhered platelets growth rate to the blood flow velocity using DPD method.In our model the boundary conditions in a Poiseuille flow were considered periodic along with the flow direction which is initially free of platelets. The platelets are modeled as rigid spheres by grouping the DPD particles. The modeled platelets can be in three different biological states: passive, triggered and activated. In passive state, platelets are not adhesive; this is a normal state of the platelets in blood. If a passive platelet interacts with an injured wall or an activated platelet, it becomes triggered and after the activation delay time - a time interval required for a passive platelet to go through the activation process and develop its ability to adhere - it is activated and becomes adhesive. This biological interaction was taken into account when two repulsive and two other attraction forces were applied in addition to DPD conventional forces. The activation delay time was confined in a specified range and was chosen in a random manner uniformly.We found that the exponential aggregation growth rate initially rose with the blood flow rate, reaching to a peak and for higher flow rates it would then fall. This was ascribed to the effect of the activation delay time. At higher flow rates, more activated platelets escaped from the primary thrombus. We detected an early (up to about 3 seconds) phase of rapid growth of the thrombus, a result which has never been discerned experimentally due to the difficulty of seeing a distinctly mural grouping of so few platelets. Key words: Platelet Aggregation, DPD method, Growth rate coefficient, Clot size.