A theoretical study on ultrasonic guide waves generated by a pulsed laser was presented,using the finite element method(FEM).Taking only the thermoelastic excitation into the consideration,and with the three dimensional axis-symmetric model,we got the temporal characteristics of the ultrasonic guided waves generated by the pulsed laser with the different beam radius and the various rising time.Furthermore we introduced the Wigner-Ville theory to analysis the distribution of the energy of the SAW in the frequency domain.The results show that the maximum amplitude of the guide wave becomes larger and larger as the beam radius of the pulsed laser decreases;In addition decreasing the beam radius can also enhance the frequency bandwidth of the guide wave;nevertheless,the varied pulse-width has no obviously influence on the temporal and frequency domain features,which are very important in the improving the generation efficiency of the ultrashort pulsed laser ultrasonics.