In order to study the heavy metal elements in liquid by double pulse laser induced breakdown spectroscopy, double pulsed laser induced breakdown spectroscopy (DP-LIBS) was used, the LIBS characteristics of Cu elements in a vertical flow of aqueous solution of CuSO4 were measured and analyzed. Two Q-switched Nd:YAG lasers operating at 532 nm was utilized to generate plasma on a flowing liquid surface, and plasma signal by detecting the CCD grating spectrometer. The gate delay, the delay time between two lasers of DP-LIBS were investigated experimentally. The results show that the intensity and SNR of Cu emission lines excited by double pulse is about 2 and 3.3 times than the intensity of line emission excited by the single pulse separately. When the delay time between two lasers at 2～3μs, emission line intensity reached maximum enhancement. The detection limit of metal ion in water solution under the optimized operation conditions was found to be 9.87 mg/L for Cu, which is about 6 times than single pulse. The results provide a basis for rapid detection heavy metals in water solution using DP-LIBS technique.