Thermal effects in solid-state laser materials are a critical issue for designing diode-pumped solid-state lasers, the temperature distribution with different pump beam transverse profiles by using finite element method on 3–5μm solid-state laser are give in this paper. Based on the theoretical analysis, the thermal focal length of Tm: YAP crystal "b" direction and "c" direction are also given in this paper. Otherwise, the aging test for 3–5μm solid-state laser is developed, and the aging test results show that the lifetime of 3–5μm solid-state laser is reach to 134 hours.