An instant detection system of a vehicle is provided. The vehicle has wheel assemblies and a brake system, and the wheel assemblies are coupled with the brake system. The instant detection system includes temperature detectors, rotational speed detectors, acoustic detectors, an analysis host and an alarm device. The temperature detectors are disposed on the brake system, and the acoustic detectors and the rotational detectors are disposed adjacent to the wheel assemblies for respectively detecting temperature information and sound information of the wheel assemblies and the brake system, and speed information of the vehicle. The analysis host is coupled with the above-mentioned detectors to receive and analyze the temperature, the sound and the speed information, so as to generate alarm information. The alarm device generates breakdown information according to the alarm information.