20 kW circular microwave drying apparatus is designed in order to dry the Shanghai Green Vegetable, the designed microwave drying apparatus contains microwave generator, dehumidification system, electrical cabinet, parabolic waveguide, control system, microwave leakage inhibited mechanism and other components. The parabolic waveguide can make microwave transmitted uniformly, combined power is used and reduce the cost. According to the working characteristics of a microwave device, PLC and infrared temperature control system are employed in control system and automated production can be realized. The drying experiment is carried by the designed apparatus, from the setting-to-work test, the design was success.