The invention provides a recursive least squares technology-based laser absorption spectrum harmonic signal peak point extraction method. The method comprises the following steps: 1, inputting the harmonic signal sampling points of a laser absorption spectrum and the sequence number of the sampling points, and fitting the main peak part of harmonic signals through using a cubic polynomial; 2, calculating an initial value by using first group input data; 3, increasing measured data, substituting to a recursion formula, and calculating; 4, calculating the peak point of a fitting function by using the above obtained recursion result; and 5, determining the calculated peak point, judging the peak point of the fitting function as the peak point of harmonic signals if conditions are met, and returning to step 3 if the conditions are not met. The method is used to search the peak point of the harmonic signals in a laser absorption spectrum monitoring system to make the monitoring system have the advantages of accurate measurement and greatly improved measurement speed, and has wide application prospect.