The invention provides a 77GHz millimeter wave radio frequency device and a using method thereof, and belongs to the technical field of millimeter wave radars. The 77GHz millimeter wave radio frequency device comprises a digital signal processor, a direct digital frequency synthesizer, an up-converter, a power amplifier, a buffer, a transmitting antenna, a receiving antenna, a low noise amplifier, a frequency mixer at a receiving terminal, a variable gain amplifier and a demodulating analog-to-digital converter. The 77GHz millimeter wave radio frequency device has the advantages that the 77GHz millimeter wave radio frequency device can be widely applied to millimeter wave range-and-speed measuring radar systems, and 77GHz is adopted as a working frequency band of a millimeter wave radar and combined with a phased-array antenna technology that low temperature co-fired ceramic (LTCC) is used as a substrate to manufacture each micro-strip patch antenna serving as an antenna unit; the direct digital frequency synthesizer is adopted and combined with an up-conversion technology to generate linear frequency modulated continuous waves; and a plurality of transmitter units are adopted andcombined with the phased-array antenna technology to realize horizontal scanning of millimeter wave beams.