A three-dimensional finite element thermal analysis model is presented for a micro-channel heat sink packaged semiconductor laser diode array(LDA). The transient and steady-state temperature distribution of the laser diode array is simulated when it works under the condition of 20% high duty cycle. It is found that the temperature of the active region rises slowly within the first few dozen microseconds after turning on current. And then,the temperature rises rapidly due to the heat flux interleaving between adjacent emitters,and finally a steady state is reached due to the thermal relaxation and accumulation effect. The static temperature distribution presents periodicity as the same of the array structure and no temperature difference exists among each emitter. The temperature rising concentrates in the electrode region of the active layer,and the temperature drops rapidly in the insulated region. The emitting facet has a higher temperature,and a max 3 K temperature difference exists along the cavity when the working current is 180 A. The output characteristic of the laser diode array is measured when it works under different currents. The temperature rising of the active region and the steady-state thermal resistance are basically coincident with the simulation.