Elevator door monitoring system, elevator system and elevator door monitoring method

The present invention relates to a system for monitoring an elevator door, an elevator system, and a method for monitoring an elevator door. The elevator door has an open state or a closed state implemented by moving along an elevator sill. The system for monitoring an elevator door includes: one or more imaging sensors configured to collect image data and depth data of at least one section in the elevator sill that is exposed when the elevator door is in the open state; and a data processing device in communication with the imaging sensor and configured to receive and process the image data and the depth data to determine whether an obstacle preventing the elevator door from entering the closed state exists in the section. By applying the present invention, the safety of the elevator door can be improved effectively, and equipment property losses and personal injuries can be avoided.