In this paper,the parameters of a Ti: sapphire laser and their correlation have been studied bssed on the Gaussian theory.The nonlinear effect of Kerr lens has been considered for the first time.According to the theoretical results a laser resonator was designed for our experiment,from which emitting of the fundamental mode with a maximum output energy of 77.3 mJ,tuning range of 650～1039 um and the divergence of about 1 mrad have been obtained.