A thick-screen frequency selective surface (FSS) with circle slot elements is designed. Based on the moment method simulation, we investigate mainly the transmission properties of this structure under no dielectric condition, when some parameters, including the element diameter, unit distribution period and incidence angle of electromagnetic wave,are changed. The result of numerical analysis show that the unit diameter, unit spacing and incidence angle have great influence on the transmission properties of the thick-screen FSS,but unit diameter has little influence on the center frequency.