The thermal characteristics of three kinds of thermal spreading boards with high-power AlGaInP LEDs were analyzed by finite volume thermal simulation method,transient thermal resistence measurement and the relationship of heat sink temperature and peak wavelength. With the same type and configuration of AlGaInP LEDs on the three kinds of thermal spreading boards, the difference lies in thermal spreading channels and materials. Transient temperature response curve is measured from which structure functions are extracted to evaluate the thermal resistance and the thermal capacitance in the heat flow path. Based on the structure function, thermal problem during the heat flow path can be easily located. The electroluminescence spectra of AlGaInP LEDs with different thermal spreading boards under various electrical currents were investigated. In terms of the relationship of heat sink temperature-peak wavelength, the thermal characteristics of samples can be qualitatively estimated. By comparison, thermal simulation and testing offer important evidence for the optimization and design of the most suitable thermal spreading model for ceramic boards.