The vortex tube is a simple device for separating a compressed fluid stream into two flows of high and low temperature without any chemical reactions. Recently, vortex tube is widely used to local cooler of industrial equipments and air conditioner for special purpose. The phenomena of energy separation through the vortex tube were investigated to see the effects of cold flow inlet-outlet ratios and partial admission rates on the energy separation experimentally. The experiment was carried out with various cold flow inlet-outlet ratios from 0.28 to 10.56 and partial admission rates from 0.176 to 0.956 by varying input pressure and cold air flow ratio. To find best use in a given cold flow inlet-outlet ratio and partial admission rate, the maximum temperature difference of cold air was presented. The experimental results were indicated that there are an optimum range of cold flow inlet-outlet ratio for each partial admission rate and available partial admission rate.