The utility model discloses a cup and aims to provide a heat-preserving cup. The heat-preserving cup comprises a cup body, wherein the cup body comprises the cup wall and a cup cover which are connected through screw threads, wherein a shell which can completely wrap the cup body is arranged outside the cup body and consists of an upper shell and a lower shell which are similar to a half of a capsule; and the upper shell and the lower shell are detachably connected with the cup body. The shell similar to a capsule and arranged outside the heat-preserving cup can be detached to serve as two drinking cups, so that the heat-preserving cup is more sanitary and convenient than the heat-preserving cup or a cup cover which are directly used by a user to drink water. A temperature displayer is arranged in the cup, so that the user can directly know the temperature of the water in the heat-preserving cup, and the mouth or the tongue is prevented from being burnt when the user directly drinks water with over high temperature.