The present invention provides a fixing seat of main transmission shaft of a scanner, wherein a conical hole is formed on the surface of a main transmission shaft whereon a scanning head can move, and a belt conveyor is used to wind around a timing pulley and an idle pulley. The timing pulley is driven to rotate by a motor device so that the belt conveyor can drive the scanning head to move on the main transmission shaft. One end of an axis of the timing pulley protruding out of the surface thereof forms a slanting conical end, which is fixed in the conical hole. The present invention has the advantages of high stability, good reliability, and a low manufacturing cost.