The present invention relates to a method for cutting brittle materials by laser, comprising the following steps: providing a first laser beam; filtering and shaping the first laser beam into a second laser beam with a predetermined energy density profile by a space filter; modulating and shaping the second laser beam into a third laser beam of elongated light spot shape; and heating the brittle materials by the third laser beam and applying a coolant on a location of the brittle materials having a predetermined distance from the trailing end of the third laser to ensure that the brittle materials undergo crack growth along the moving direction of the third laser beam; wherein, the third laser beam is provided with a leading end and a trailing end; the average gradient of the energy density profile of third laser beam at the leading end is less than that at the trailing end. The present invention also provides a device adopting the method for cutting brittle materials by laser.