Abstract: A coordinate transformation method for a user and an interactive system including a detection module is disclosed. The coordinate transformation method includes determining a face information and a command object of the user via the detection module to obtain a face coordinate and a command object coordinate, transforming the face coordinate into a transformed face coordinate according to a coordinate of the detection module, obtaining an angle between an optical-axis ray and a line formed via connecting the transformed face coordinate and the coordinate of the detection module, obtaining a transformed command object coordinate according to the angle and the command object coordinate, and determining a depth change of the command object according to the transformed object coordinate to set up an interactive operation between the interactive system and the user.