Disclosed herein is a quantitative analysis method for measuring a target element in a specimen using laser-induced plasma spectrum. More particularly, the present invention relates to a method for analyzing a composition ratio of a target element by calculating peak intensities when peaks overlap each other in a spectrum, and a method for selecting a peak of a wavelength at which the highest precision and reproducibility are secured through linearity of a correlation plot of the peak intensities and a value by dividing a standard deviation value of calibration curve data (peak intensity ratios) by a slope when an internal standard method is used for quantitative analysis of a target element.