LIBS (laser induced breakdown spectroscopy) combined with the signal acquisition device of gated PMT(photo multiplier tube) technology is one of the key components that affect the miniaturization and integration of the LIBS analysis system. Therefore, a 12 bit PMT signal high-speed acquisition system with a 7.6 MHz acquisition frequency was designed and implemented using a microcontrol chip and an AD9226 chip. The element lead(Pb) and chromium (Cr) were quantitatively analyzed. The experimental results show that LIBS combined with Gated-PMT analysis system adopts high-speed acquisition system to establish Pb, Cr element calibration curve fitting degree is 0.988, 0.978, relative standard deviation is 3.56%, 6.57%, detection limit is 0.013 mg/L and 0.087 mg/L, respectively. Compared with the LIBS detection technology without PMT, it is an order of magnitude lower. Compared with inductively coupled plasma-mass spectrometry, the relative errors of Pb solution with 7.0 mg/L and Cr solution with 0.7 mg/L were 2.81% and 3.26%, respectively. Therefore, the PMT signal high-speed acquisition system has a good quantitative effect in the LIBS analysis of heavy metals in aqueous solutions, and has the advantages of small size, low power consumption and low cost, which is conducive to further promoting the application of LIBS technology in the field of water quality heavy metal detection.