The invention discloses a combined polished rod sealing device for an oil well. The combined polished rod sealing device for the oil well is composed of a pressing cap, a centering sleeve and a stair-shaped sealing pipe, a sealing cavity for storing a filler is formed in the sealing pipe, and the upper end of the centering sleeve and the upper end of the sealing pipe are connected in a threaded mode; the pressing cap comprises an inner pipe and an outer pipe, the inner pipe and the outer pipe are formed through integrated casting, the inner side of the inner pipe is in threaded connection with the upper end of the sealing pipe, and the inner side of the outer pipe is in threaded connection with the lower end of the sealing pipe; and meanwhile the device further comprises a pressure injecting device and a material injecting device which longitudinally penetrate through the pressing cap and the centering sleeve. According to the combined polished rod sealing device for the oil well, the pressing cap adopts a double-layer threaded connection structure, and thus connection between the pressing cap and the sealing pipe can be greatly reinforced; and meanwhile an externally-connected material injecting structure is adopted for automatic material injecting, and filling of the filler is greatly facilitated.