A practical method to design the heat dissipation system of the three phase photovoltaic Grid-connected inverter was presented.the switching losses of the IGBT module used in the inverter were calculated.A practical formula to calculate the heat resistance of heat dissipation system was given.A heat dissipation system for the inverter using forced-air-cool was designed.The calculated results and the experiment results verify the validity and practicability of the presented design method.