Based on the working characteristics of the pulsed laser diode (LD) end-pumped composite crystal, a finite element thermal model of the pulsed LD pumped YAG/Nd∶YAG composite crystal was established using the heat conduction theory to solve the thermal effect caused by the LD end-pumped crystal. The effects of pump power, undoped crystal thickness, and pulse width on the temperature field and thermal deformation of the composite crystal were quantitatively analyzed. The results show that when the thickness of the doped crystal is 8 mm, the thickness of the undoped crystal, pulse width, and repetition rate is 3 mm, 3 ms, and 100 Hz, respectively. Furthermore, the radius of the pump spot collimated and focused by the optical coupling system is 300 μm when a pulse with a pump power of 80 W is applied. In the LD end-face pumped composite crystal YAG/Nd∶YAG, the highest temperature and maximum thermal deformation available at the center of the end-face pumped are 66.84 ℃ and 0.12 μm, respectively. It is thought that the composite crystal can effectively reduce the high-temperature rise of the crystal and the thermal deformation of the end-face of the crystal. This conclusion provides theoretical guidance for realizing the high power output of a Nd∶YAG laser.