An automotive radar device and an antenna cover are disclosed. The automotive radar device includes a base, an antenna disposed on the base, and the antenna cover. The antenna cover includes a main portion and an engagement portion connected to the circumference of the main portion. The engagement portion can be engaged to the base such that the main portion covers the antenna. Therein, a thickness of the main portion along a radiation direction of the antenna is equal to half-wavelength corresponding to a center operation frequency of the antenna under a dielectric constant of the main portion. Thereby, energy radiated from the antenna can mostly pass through the main portion without excessive signal attenuation, which solves the insufficient signal intensity due to a protection cover in the prior art. Further, the main portion can be made of flexible and weather resistant material to improve its physical and chemical properties.