Nowadays, the atrium has become one of the remarkable and functional architecture elements in many building designs. The form of atriums as a special feature in contemporary buildings was from the enclosed courtyard of ancient buildings. As the development of architectural techniques continued, atriums have been used broadly in modern buildings. When architects would like to apply the atrium into their designed building, factors such as geometry design, daylighting design, thermal and ventilation systems design should be considered. Among these factors, daylighting performance and atrium geometry are the determinant parts which are related to the daylight in the atrium. The daylighting performance of an atrium also supplies an irreplaceable function to the interior space of the building and saves much energy for lighting. This paper presents a study on the geometric effect on the atrium daylighting that was based on the DF(Daylight Factor) values of four geometric atrium models (square, rectangular, triangular and polygon) which were built in ECOTECT. Meanwhile, the geometry of the section in each atrium was changed by alerting the height of atrium storeys. For each atrium model, it has been assigned with the corresponding reflectance to the surfaces, floors, interior walls and the base. Daylight values were measured at three points across the atrium base: centre, half way along the edge and the corner position. At the same time, there are three kinds of window proportions set on interior walls of the atrium for the simulation. All simulations were operated in a CIE overcast sky condition in ECOTECT.