The invention discloses a method and a device for detecting trace metal elements in a water body by using the laser-induced breakdown spectroscopy assisted by direct current discharging vaporization. High voltage direct current discharging is utilized to vaporize a liquid sample, the vaporized sample is separated through a separation device, gas is injected to a graphite bearing piece, the graphite bearing piece containing elements to be detected is subjected to pulse laser ablation induction to generate plasma and transmit spectroscopy signals, and finally a spectrograph is utilized to conduct detection analysis to measure the trace metal in the water body. By means of the method and the device, the pulse laser sample ablation efficiency is greatly improved, the detected spectroscopy signals are greatly strengthened, the detection sensitivity is improved, the detection limit of the metal elements is reduced, and the method is feasible for online high-efficiency quick detection of the metal elements in the water body.