Pulsed laser frequency locking method based on molecular absorption is proposed to meet the requirement of Rayleigh high spectral resolution lidar for the frequency stability of pulsed laser emission unit. We construct a pulse laser frequency locking system based on the principle of iodine molecule absorption spectrum, using the GHz magnitude peak holding circuit, proportional integration differential (PID) control algorithm and temperature control system with accuracy of ±0.02 K. First, the accurate temperature-controlled iodine molecular absorption pool is measured by using BBO (β-BaB₂O₄) crystal frequency-multiplied 532 nm continuous laser, and the absorption spectra of its 1109 line at different temperatures are obtained, so as to determine the frequency discrimination curve. Second, using the fitting equation of frequency discrimination curve, the quantitative relationship between the change of pulse laser energy and the frequency shift and the measurement sensitivity are obtained. Finally, the PID control algorithm is used to compare the difference between the set value of frequency and frequency shift, and the difference is fed back to the seed laser in the form of voltage. The frequency shift of the pulse laser is compensated by changing the frequency of the seed laser, and then the dynamic frequency locking of the pulse laser is realized. The experimental results show that the frequency shift of the pulsed laser is less than ±2.2 MHz within 25 min, which can make Rayleigh high spectral resolution lidar achieve wind measurement error less than ±0.6 m/s and temperature measurement error less than ±0.5 K.