A method and a system for determining a datum plane are disclosed. The method for determining a datum plane includes: acquiring a depth image; performing edge extraction on the depth image to form an edge image, the edge image including a plurality of planar graphs; and selecting from the planar graphs in the edge image to determine the datum plane. The technical solutions provided by the disclosure can easily match the virtual object with the real scene in real time, and improve users' sensory experience beyond reality.