In order to improve the detection accu racy of coaxial optical path double-beam laser-induced breakdown spectroscope (DB-LIBS) in detecting heavy metal of soil,parameter optimization of testing setup has been done.The heavy metal Pb in soil is set as the detection target in the experiment.First,the characteristic spectral intensity of Pb in so il under double beam is enhanced by 2-3times than the single one which is gained from the comparative test with 120m J working energy of a single pulse.Then,delay time between two laser pulses is set as 0ns,50ns and 100ns ,the spectrum acquisition delay time is increased from 2.6μs to 5.2μs by increment of 0.2μs,and experiment is done in 14spectrum acquisition time delays under each laser pulse delay time to obtain the spectrum information of Pb element at 405.78 nm.And the best laser pulse delay time and spectrum acquisition delay time are 50ns an d 4.6μs,respectively,which are obtained from consideration of both characteristic spectral intensity and signal to background ratio in the results of the experiment,and the relative standard deviation reaches 0.10.So,it is demonst rated that the parameter optimization is good for improving the detection accuracy of coaxial optical path DB-LIBS syste m.