Abstract: In order to research the effects of frequency bandwidth on the propagation and applications of broadband laser, the propagation formula of broadband laser with rectangular spectrum passing through a bifocal dispersion lens system was derived by using diffraction integral. Bandwidth-induced focal switch in broadband laser with rectangular spectrum is studied by numerical calculation. The effects of bandwidth on the intensity distribution and focal switch were analyzed. The results show that bandwidth is an important factor affecting intensity distribution and focal switch. Primary maximum intensity of the focused broadband laser can rapidly bounce from one place to another with the variety of bandwidth and then the focal switch is generated. The results are helpful for further applications of broadband laser.