The invention concerns a method for controlling automatic transmission (3) of a vehicle comprising an engine (2) driving the transmission (3) which consists in: detecting a downhill situation of the vehicle, and selecting a transmission ratio so that the engine absorbs energy, storing a longitudinal speed of downhill start (Vmin) when the vehicle starts going downhill, and while the vehicle is running downhill, comparing the current speed (V) of the vehicle with the downhill start speed (Vmin) such that the current speed (V) exceeds the downhill start speed (Vmin) by a predetermined difference (VS), then controlling the transmission to trigger downshifting.