The present invention discloses a method for quantitative analysis of elements in an unknown sample by spectrum combined with mass spectrometry. Laser-induced breakdown spectroscopy is combined with secondary extraction field time-of-flight (TOF) mass spectrometry for quantitative analysis, and quantitative analysis for high-detection-sensitivity, real-time, fast, high-precision, non-contact simultaneous detection of multiple elements in one sample can be realized without sample pretreatment. Dual wavelength laser in the method helps to ionize photofragments and molecular clusters again, improves mass signal stability, and enhances laser plasma emission spectroscopy signals; a secondary extraction field in the method helps to improve TOF mass spectrometry resolution and optimize signals. The time-of-flight (TOF) mass spectrometry in the method can be used to quickly determine the elements in the unknown sample to save analysis time and realize real-time quantitative analysis, and also can correct influence of matrix effect and surface morphology on quantitative spectrometric analysis, dark state species which cannot be detected by emission spectra can be detected, and the accuracy of the quantitative analysis can be improved.