A laser-cutting device for cutting brittle basilar plates includes pre-cutting systems, laser optical system and cooling system, said pre-cutting system is used for forming pre-cutting line on the basilar plates; said laser optical system is used for producing laser light, and the laser light heats the basilar plates along the pre-cutting line to making the basilar plates thermal expansion; said cooling system is used for cooling said thermal expanding basilar plates; said laser optical system includes laser cavity generating said laser light and optical path adjustment system, the optical path adjustment system is equipped on the optical path on the basilar plates and illuminated by said laser light to adjusting the length of the optical path, so it can adjust the size of laser light point to meet different cutting needs.