In this work, a steady-state heat transfer equation in a side-pumped Nd:YAG laser rod was solved numerically using finite element method (FEA). The resulting temperature and stress distributions were calculated under the condition of totally and partially direct side pumping structures with LASCAD software. From the result of simulation, we compare between the different pumping lengths, and mainly indicate the effect of pumping lengths on the temperature distribution, stress, displacement and the optical path difference (OPD).