In order to study the influence of delay time on laser-induced breakdown spectroscopy(LIBS), the relationship between the intensities of the spectral line and the delay time was discussed in theory, and the LIBS instrument manufactured by Applied Spectra Inc was used for testing the limestone certified reference sample GBW07716. The characteristic spectral line was analyzed with MnⅠ357.788 nm, WⅡ364.141 nm, WⅠ407.436 nm, WⅠ426.938 nm and CoⅠ387.312nm.It was demonstrated that the intensities of the spectral line decrease exponentially with the delay time, and the decrease speed is not the same for different spectral line. The intensities of the ion spectral line are stronger in an early stage, but decrease faster with the increase in delay time than the atomic spectral line. The experimental data fit with exponential law and the fitting R value is about 0.99.