The invention provides a heat dissipation control method and device for a vehicle-mounted fuel cell, belongs to the technical field of fuel cell temperature control, and aims to solve the problems that heat dissipation control in the prior art is relatively high in difficulty and cannot be compatible. The method comprises the following steps that: the real-time water temperature at a cell stack cooling liquid outlet at the current moment is acquired; the difference value between the real-time water temperature and target temperature is input into a temperature control model, the initial rotating speed of a cooling fan is obtained, and the cooling fan is controlled to be started and operates at the initial rotating speed; the real-time water temperature change at the cell stack cooling liquid outlet after the cooling fan operates is monitored; according to the real-time water temperature change, whether the current working condition meets a feed-forward updating requirement or not is judged, if the current working condition does not meet the feed-forward updating requirement, feed-forward parameters in the temperature control model are kept unchanged, and the cooling fan is controlled to operate at the original rotating speed, and otherwise, the feed-forward parameters are updated according to a preset rule, the new rotating speed of the cooling fan is obtained, and the cooling fan is controlled to operate at the new rotating speed. The method and device can automatically adapt to factors such as environment temperature, vehicle speed, altitude and the like.