The invention discloses a microwave power testing device based on a universal serial bus (USB) interface. The microwave power testing device comprises a casing, a circuit board support, a microwave sensor, an analog circuit board and a digital circuit board, wherein the analog circuit board and the digital circuit board are connected through a high-density connector, the analog circuit board comprises a chopping amplifying circuit, a rear-stage amplifying circuit, an analog-to-digital converting circuit, a zero calibration selection circuit and a temperature analog-to-digital converting circuit, the digital circuit board comprises a digital signal processing circuit, a USB interface circuit and a power source management circuit, and the digital signal processing circuit comprises a digital signal processor, a synchronous dynamic data storer, a flash memory program storage and a complicated programmable logic array chip. The microwave power testing device is compact in structure, small in size, light in weight and flexible in programming, adopts USB power supply, can be connected with computers with USB host interfaces or other electronic measuring instruments, can form a microwave power automatic testing system rapidly and is suitable for applications in places of laboratories, fields, production lines and the like.