The most important role of V2X technology is to significantly enhance driving safety. This paper proposes an omnidirectional collision warning method based on vehicle to vehicle communication. The warnings are divided into two categories: forward collision warning (FCW) for vehicles moving in the same direction and cross collision warning (CCW) for vehicles moving in different directions. With the Basic Safety Message (BSM), the driving states of vehicles which communicate with host vehicle can be obtained. For vehicles which moves in the same direction, the lateral offset of the two vehicles, the time to collision (TTC) and time headway (THW) are used to estimate forward collision risk. For vehicles which moves in different directions, time to the closest point approach (TCPA) model and the separating axis theorem (SAT) are used for cross collision detection. With the methods above, nine applications are realized which include static vehicle reminding, slow vehicle reminding, close car-following distance reminding, forward collision warning, retrograde vehicle reminding, cross collision warning, left-turn assist, entry of vehicle from auxiliary road reminding and collision inevitable warning. The effectiveness of the method is verified by a series of experiments on real roads. The misdiagnosis rate and omissive judgement rate are analyzed. Compared to traditional methods, the danger detection rang are much wider and the danger in different directions can all be detected. Moreover, the calculation of lateral offset can obviously reduce misdiagnosis rate. It is worth mentioning that the effectiveness of the method relies on the accuracy of GPS positioning accuracy. The higher the GPS positioning accuracy is, the better the method works.