The present disclosure provides an emergency braking system, an emergency braking method and a semitrailer, capable of improving the braking effect of the vehicle, thereby achieving improved safety for the vehicle. The system includes: a sensor component configured to collect sensed information on an environment where a semitrailer is located; and a braking controller configured to determine whether there is a risk of collision for the semitrailer based on the sensed information, and if so, calculate a maximum adhesive force that can be provided by a road surface the semitrailer is currently on, determine a first braking pressure corresponding to each wheel based on the maximum adhesive force and axle load information, and transmit to a braking system a first braking instruction carrying the first braking pressure for each wheel.