The invention discloses a storage box on a roof. The storage box on the roof comprises a vehicle main body and a storage device, wherein the storage device is arranged on the vehicle main body; the storage device comprises the storage box, a rubber band and a guide groove; the storage box comprises a fixed storage box and a mobile storage box; the fixed storage box is connected with the mobile storage box through the rubber band; the fixed storage box is connected and fixed together with the vehicle main body; the mobile storage box is connected with the vehicle main body through the guide groove; and the guide groove is formed in the vehicle main body. An elastic block on a vehicle can buffer impact force of the mobile storage box so as to avoid collision between the mobile storage box and the fixed storage box; as the elasticity of the rubber band on the vehicle is great, a user can put luggage, which cannot be put in the vehicle, into the storage device; and moreover, the storage device can enlarge the storage area by using the tenacity of the rubber band so that the user can take more luggage; and finally, the luggage is bound together with the storage box by using the rubber band or a rope; therefore, the storage box on the roof facilitates travels of the user.