In order to improve the precision and sensitivity of laser-induced breakdown spectroscopy device on detecting heavy metal, parameter optimization should be done. After selecting the initial delay time parameter in detecting navel orange experiment of laser-induced breakdown spectroscopy device, a cell range from 1.10 to 1.30 μs of delay time containing the initial parameter was extracted and experiment on it was conducted. There are more than one peak in the curve of element line intensity and signal-to-background ratio vs the delay time in the cell range, and the peak values are higher than the initial one. Confidence interval of the delay time calculated indirectly by interval estimation in Statistics is (1.13, 1.25］. The relative standard deviation decreases from 0.103 269 548 to 0.025 322 279 5 when the delay time adjusted from 1.20 to 1.14 μs in the confidence interval. It is suggested that parameters range of LIBS experimental device can be adjusted freely in the range while detecting measured elements so as to improve the precision and sensitivity.