A short-range inter-vehicle communication and warning apparatus comprises a forward radar and a backward radar. The apparatus uses the radars to generate Frequency Modulation/Continuous Wave (FMCW) signals, uses amplitude shift keying for data modulation and arranges a special packet format, to realize such a low cost and fast response device of collision avoidance for vehicles. The invention has the dual capabilities of detecting and communicating simultaneously. It can also measure the relative speed of a preceding/rear vehicles and the relative inter-vehicle distance. The invention also exchanges the real-time traffic information with the preceding/rear vehicles at the same time. It is applicable to a one-to-one or one-to-many inter-vehicle channel model.