Abstract: An off-line data synchronization method was proposed to solve the problem that attitude data of measuring while drilling system of an ordinary medium or small rotary drilling rig cannot be uploaded on-line. In the method, hole synchronizer and exploring tube at bottom of the hole are used to collect real-time drill-pipe data and attitude data of the borehole respectively during drilling process; after drilling, the synchronizer reads all the attitude data from the exploring tube, and then selects the effective measuring points to drawing trajectory by linking these selected points. Test results show that the off-line data synchronization method realizes synchronization of borehole data and attitude data, can fully meet demands of measurement while drilling of the ordinary medium or small rotary drilling rig without any change of structure of the drilling rig.