Based on the theory of semianalytical thermal analysis, the temperature field and thermal lens effects within a diode-end-pumped Nd:YAG rods were investigated. A general expression of the temperature field within Nd:YAG rods was obtained through the analysis of a diode-end-pumped Nd:YAG rod, using what we believe to be a new method to solve a heat conduction equation of isotropic material. Calculating the thermal focal length within the diode-end-pumped Nd:YAG rods was done by an analysis of the additional optical path differences caused by heat, which was in good agreement with experimental results. These results show that the maximum temperature on the pump face of Nd:YAG rods is 51.9°\text{C} and the thermal focal length is \text{22 .4 \hspace{0.17em} cm} when the output power of the diode laser is 10 W. Under the same conditions, the experimental value of the thermal focal length is \text{21 .0 \hspace{0.17em} cm} . The difference between the theoretical analysis and the experimental result is only 6.7%. Results from this work can provide the theoretical basis for the optimized design of diode-end-pumped all-solid-state lasers.