Chloromyia formosa can reach a length of 7.3–9 millimetres (0.29–0.35 in) and a wing length of 6–7 millimetres (0.24–0.28 in). Their body is elongated, the thorax is metallic green, the head is hemispherical without hair, while the eyes are quite hairy. Antennae are short, the first antennal segment is longer than the second. The legs are black, only the knees are yellow. The abdomen is flattened and broad.
An evident dimorphism exists between the males and the females of this species. In females, the abdomen is blue-green with a purple sheen (depending on the light), while in males it shows a copper-green sheen. The female’s eyes are separated from each other. The wings are yellowish-brown.