Drag inhibitor/reducer for drilling fluid and preparation method of drag inhibitor/reducer

The invention relates to a drag inhibitor/reducer for a drilling fluid and a preparation method of the drag inhibitor/reducer. The drag inhibitor/reducer is prepared from the following components in percentage by weight: 0.5-2% of cationic gemini surfactant, 1-2% of quaternary ammonium cationic surfactant, 0.5-1% of vulcanized oil, 20-25% of glucoside water solution and the balance of white oil. The preparation method comprises the steps of adding the vulcanized oil into the white oil at the temperature of 50-60 DEG C, and stirring for 1-2h; then, sequentially adding the cationic gemini surfactant and the quaternary ammonium cationic surfactant, and stirring for 2-4h; next, adding the glucoside water solution, and stirring for 2-4h; and finally, controlling the temperature at 100-120 DEG C, and concentrating for 1h to obtain the drag inhibitor/reducer for the drilling fluid. The drag inhibitor/reducer is suitable for reducing frictional resistance in the drilling processes of horizontal wells and large-displa