A coordinate calibrating method includes the steps of: (1) reading paper coordinates by adopting two OID sensors, comparing the coordinates read by the two OID sensors with pre-designed coordinates of paper to obtain coordinate deviation of positions of the two OID sensors, and according to the coordinate deviation, calculating an inclination angle value θ generated by the coordinates of the two OID sensors; and (2) according to the coordinate deviation and the inclination angle value, calibrating an actually read coordinate position of a pen by selecting the second OID sensor as a reference point, translating horizontally and vertically coordinates of the pen to be corrected first, and then rotating the coordinates by the angle θ with reference to the second OID sensor, so that the positions of the two OID sensors coincide with pre-designed standard positions, and the coordinate position of the pen is calibrated.