The invention discloses a one-piece dress which comprises a one-piece dress body, wherein the one-piece dress body comprises a dress body, sleeves, a collar and a skirt; openings of the sleeve of the dress body are connected with the sleeves in a knitting manner; the collar of the dress body adopts a double-collar design and comprises an inner collar and an outer collar; a round waistband is arranged on the waist part of the dress body, is in a double-layer structure and comprises an inner layer and an outer layer; a shading part serves as the inner layer; button holes are formed in the shading part; buttons are arranged at the upper end of the skirt and correspond to the button holes in the shading part; the dress body is connected with the skirt through the buttons. According to the mode, the one-piece dress is reasonable in design and easy to make; the collar is novel and attractive in design; the skirt is detachable, so that the one-piece dress can be worn by a plurality of dressing modes.