The invention discloses a single-feed-cylinder capillary rheometer. A feed cylinder of the capillary rheometer is a single feed cylinder; the front end of the feed cylinder is provided with a plunger, the rear end of the feed cylinder is provided with a traveling nut, an electric heater is arranged around the feed cylinder, a long capillary die, a support part and a zero-length capillary die/short capillary die are arranged in the feed cylinder, and the outer diameter of the long capillary die, the outer diameter of the zero-length capillary die/short capillary die and the outer diameter of the support part all are matched with the inner diameter of the feed cylinder. The single-feed-cylinder capillary rheometer can be used for measuring extensional flow and shear flow parameters of polymer melt simultaneously, can eliminate entry pressure drop well, has the same function as a double-feed-cylinder capillary rheometer, and also has the advantages of saving raw materials, facilitating dismounting, purging easily, reducing artificial influences, realizing higher precision, and the like.