The invention provides a projection method and system. The method includes providing a first sensing group sensing a space and generating a first sensing result to determine whether a user is in an entering or exiting state relative to the space; providing a second sensing group sensing a first or second object in the space according to the first sensing result and generating a second sensing result; and generating a prompt information according to the second sensing result and displaying the prompt information. The system includes a first sensing group, a second sensing group, and a display device. The method and system of the invention sense the space according to the entering and exiting state of the user to effectively reduce the inspection steps of the user for the space, thereby effectively improving the safety of the space, and improving the operating convenience of the user of the space.