Abstract: The pump LD intensity distribution model under the Gaussian intensity approximate condition was revised, and the numerical model of the temperature field was established in the crystal cylinder of diode side-pumping solid state laser. The temperature field and warming process of the transient and steady state in the laser rod by symmetrical trigonal side-pumping were simulated using the finite element analysis method. The temperature field distributions in the laser crystal of the Gaussian intensity and uniform intensity hypothesis were presented and compared, and the thermal lens focus of the crystal cylinder was measured experimentally. It is concluded that the LDA pumping structure and the non-uniformity of the cooling field make the experiment results divergent from those of the simula