With [010] orthorhombic Nd:YAP and [111] cubic Nd:YAG crystal rods as our samples for study, based on crystal symmetry, relation between thermal effects caused in pumping process and lattice symmetrical elements has been investigated. It is shown that the results obtained satisfy Newman principle.Effects of symmetry of thermal induced refringence and birefringence on isogyre pattern, depolarized losses as well as thermal focusing of crystal are also described in this paper.