A relative position positioning system includes a first apparatus and a second apparatus. Each one of the first and second apparatuses is configured to sense a relative position of the other in an initialization period. In an operation period, each one of the first and second apparatuses is configured to measure its own displacement relative to a plane, transmit its own measured displacement to the other through a wireless transmission unit, and update the relative position of the other according to its own displacement and the displacement received from the other.