Three gas separators with different structural parameters were designed and tested with air and water as the working fluid to find the optimal structure. Visualized method was used in the experiments, with a high speed video camera employed to record the separation process, aiming to find the effect of the structural parameters. It is showed that the inlet angle, outlet angle, length and number of the vanes have significant influence on the separation process. For designing a gas separator, the outlet angle of swirl vanes to the axial direction should not be over 45° and at least 5 swirl vanes with the length exceeding 45 millimeters are required.