Abstract: Isentropic light piston wind tunnel is a kind of short working duration tunnel.It is adequate to be used for the research work of instantaneous heat transfer measurement.Based on the understanding of the wind tunnel characteristics,a method for determining the sizes of its main components was presented.Pressure ratio and working time duration trun are key parameters to the determination of the tube size, and the mass of the piston depends on the allowed peak value of the matching pressure oscillation.