The invention provides an antenna downward inclination angle arrangement method and device. Function value sets corresponding to actual horizontal irradiation image functions and a target horizontal irradiation image function of a newly-arranged communication system under different horizontal azimuth angles are calculated, wherein the actual horizontal irradiation image functions correspond to the combination of the values of control channel emitted power, the antenna mechanical downward inclination angle and the antenna electronic downward inclination angle of the newly-arranged communication system, and the target horizontal irradiation image function of the newly-arranged communication system is determined based on the horizontal irradiation image function of an original communication system. When the difference between the function value set corresponding to the first actual horizontal irradiation image function and the function value set corresponding to the target horizontal irradiation image function of the newly-arranged communication system conforms to a preset condition, the values of the control channel emitted power, the antenna mechanical downward inclination angle and the antenna electronic downward inclination angle which correspond to the first actual horizontal irradiation image function serve as the actual setting values of the control channel emitted power, the antenna mechanical downward inclination angle and the antenna electronic downward inclination angle of the newly-arranged communication system. Therefore, the network building period is shortened, and the networking cost is reduced.