The invention discloses a method for improving the cutting of a nanosecond pulse width ultraviolet laser, which relates to the technical field of laser cutting. The method comprises the following steps: a polarizer is mounted in the laser output direction of the nanosecond pulse width ultraviolet laser; the current I or laser pulse repetition frequency f of the nanosecond pulse width ultraviolet laser is set as a fixed value; the laser pulse repetition frequency or current of the nanosecond pulse width ultraviolet laser is regulated, so that the laser pulse width Tpuls meets Tpuls less than orequal to Tpulsmax; the angle Alpha between the light vibration direction of ultraviolet light emitted by the nanosecond pulse width ultraviolet laser and the polarization direction of the polarizer is adjusted, so that E output is equal to E0, wherein E0 is a fixed value of laser energy absorption of thermoplastic resin material. According to the method for improving polycarbonate laser cutting under a nanosecond ultraviolet laser disclosed by the invention, the cost is low, the reliability is high, and the requirement of polycarbonate material cutting on end surface evenness, no surface color change and no turned edges is met.