Abstract: In this paper,the flat-ground-plane projection model proposed in our previous study is applied to calculate the shading and blocking loss between the neighboring heliostats. Since the effective area is influenced by the mirror surface damage,operation failure ratio and mirror cover loss,a correction factor considering those factors is introduced into the model to calculate it. Taking the heliostats field of the 200 kW solar thermal power tower plant in Suqian as the study case,the shading-blocking efficiency of the heliostats field is calculated under typical conditions of four solar term days,and accordingly the average effective area of the mirrors is obtained.