A modular microwave power supply comprises a plurality of microwave power supply modules and a plurality of isolating diodes. To upgrade the output power of the modular microwave power supply, the plurality of microwave power supply modules are connected isolatively in common to a magnetron load by the plurality of isolating diodes, such that power combining of the plurality of microwave power supply modules is achieved, and the efficiency as well as the accumulated-heat dissipating ability of the modular microwave power supply are as good as each of the plurality of microwave power supply modules.