An adaptive early warning method based on Vehicle-To-Everything (V2X) and a system thereof, wherein through a mobile communication and a short-range wireless communication technology, connection between a vehicle and a target is achieved, the adaptive early warning method for vehicles comprises steps of: establishing a first monitoring list, determining whether there is a key target among the connectible surrounding targets that reaches a collision early warning threshold, and if any, then establishing a second monitoring list to exclusively receive and monitor the vehicle location and the speed information of the key target; calculating an estimated collision time and a communication delay value; determining a warning level according to the communication delay value and the estimated collision time, and providing an early warning.