According to the limitations of desk microwave power measurement instruments used in system setup and product line field, a brand new minisize power measurement design based on USB interface is proposed. Firstly, the design principles of analog channel, digital signal processing and the USB interface for the power sensor is introduced. Then the design fundamental of the USB communication to the host is presented. The vivid implementation of the software on the DSP, USB firmware and the PC host is fully discussed. This design features small size, light weight and programmable USB interface, which supports the Interchangeable Virtual Instruments (IVI) driver and thus simplifies the program procedure. The PC based platform allows for lower cost than traditional power meters and power sensors, and with a laptop PC it is ideal for field portable power measurement and remote multi-channel monitoring applications using all kinds of USB hubs.