A simple optical system consisting of an aperture and a thin lens is considered.It is shown that when a Hermite-Gaussian (H-G) beam is incident on such a type of system and the parameters of the optical system and the beam satisfy a certain condition,a new effect called the focal switch can take place.Detailed numerical results and physical explanation are given to illustrate the characteristics of the focal switch of H-G beams.A comparison with the previous work is made and the potential application of the focal switch is pointed out.