The general solution of crystal under TEM_ 00 with rectangular section interior temperature field distribution was obtained by a new semi-analytical thermal analysis method. Subsequently some relevant parameters,which would influence temperature field distribution, were analyzed.And discrepancy between the rectangular section crystal and the circular section crystal was compared.Research results will be theoretically established for further research,such as phase mismatching induced by non-uniform temperature raise,and play instructive effect at improvement of DPSSL′s output power.