A method to measure the transient thermal diffusivity performance of a heat dissipation module by selecting two measurement points on the surface of the heat dissipation module, and locating the two measurement points at the same side of the thermal center point but different distances, and measuring the temperature of the two measurement points separately and using first equation which is the analytical solution of the energy equation. After calculating the first equation, second and third equations are used to find M. The distance X1 between M and the first measurement point and temperature T1 at a moment of transient state are also inserted into the first equation to obtain the value of the thermal diffusivity coefficient α, which represents the transient thermal diffusivity performance for the heat dissipation module.