The utility model provides a safe seating and sealing unit in back is repaiied to screw pump belongs to the oilfield equipment field. The lower extreme of this seating and sealing unit links to each other with tubing hanger, tubing hanger's lower extreme is connected oil pipe and stretches into the cover intraductally, even there is the cross flange sleeve pipe upper end, the seating and sealing unit includes the jack, bear dish and four lead screws of erectting the setting, in the bottom entry cross flange of lead screw, it runs through the jack that bears set both ends to bear to coil to have, insert in the jack upper end of lead screw, in the bottom entry cross flange of lead screw, the last lower extreme of lead screw all has threaded connection to have fixation nut, the jack is located and bears between dish and the tubing hanger, the top top of jack is leaned on in bearing a set lower part, the bottom of jack is sat on tubing hanger, tubing hanger is last to have the sealing, tubing hanger is located the lower extreme of jack, the big cross centrum of tubing hanger has on the cross flange, the sealing can be sat and realize sealing in the big cross centrum of tubing hanger. This device structural design is ingenious, and the security performance is high.