This paper reports first our comparative study on the qualitative performance of varied prosthetic valves in current use It showed that the bileaflet mechanical valve is the optimum valve prostheses,but with disadvantages of a narrow central channel and big peak backflow.The author based on the above results designed a model of downstream direction bileaflet mechanical valve and used finite bulk method to calculate the velocity and shear stress profiles of this valve.The results showed that both the velocity and shear stress profiles obtained were of much better quality.