A light-emitting device having a cover (1), a heat sink (2) and a light-emitting assembly (3), wherein the heat sink (2) has at least one first locking part (a), the cover (1) has at least one second locking part (b) corresponding to the first locking part (a), the second locking part (b) engages with the first locking part (a) to form an enclosed cavity (5) for the light-emitting assembly (3), and the second locking part (b) has a pressing part (b1) pressing the light-emitting assembly (3) against the heat sink (2).