Through analysis for the performance features of laser diode array end pumped disk laser amplifier,a finite element thermal model of laser crystal Nd∶YLF is established.3D and transient distributions of temperature and thermal stress in repeated pulse laser crystal were calculated when pumped by kilowatt grade and 520μs duration.The result shows that fracture due to thermal stress may occur when effective pump energy is up to 10kW/cm2 and the increase of heat transfer coefficient can reduce the temperature but may increase the maxim thermal stress.