Laser-induced breakdown spectroscopy (LIBS) as a rapid spectral analysis technology shows the outstanding application foreground and research value in coal quality on-line monitoring. In the practical application of this technology, the pulsed laser power fluctuation leads to the worse performance of long term stability, so a closed-loop feedback pulsed laser power locking device is set up, using laser power feedback signal to control and lock Nd∶YAG laser output power. The laser power locking experiments are investigated in the same pre-set value with different splitting ratios, the different laser output power with the same proportion and the long time running modes. The results show that the beam split ration has little impact to the stability of the laser power, and the smaller split ration leads to the faster stabilization. This device can keep the output power of the pulsed laser being locked in the pre-set range for a long-term running, RSD values decrease from 2.4% of free-running to 1.1%.