The invention discloses a rail-vehicle-based air conditioner control method and device, wherein the method comprises: controlling operating frequency of an air conditioner of a rail vehicle through a target refrigerating or heating capacity control mode, wherein the target refrigerating or heating capacity control mode controls the operating frequency of the air conditioner of the rail vehicle according to a difference between the target refrigerating capacity and actual refrigerating capacity or a difference between the target heating capacity and actual heating capacity; over preset time, switching to a target temperature control mode to control the air conditioner of the rail vehicle. The technical problem of the prior art is solved that the use of target temperature control mode in a rail vehicle leads to a change in the interior temperature upon a passenger's boarding and alighting.