The invention discloses an oil mist concentration alarm method and device. When it is monitored that the rotating speed and the oil supply amount of an engine reach a preset interval at the moment ti,the oil mist concentration value f (ti) = OMC (ti) at the moment is recorded, and when it is monitored that the rotating speed and the oil supply amount of the engine reach the preset interval againat the moment tj, the oil mist concentration value f (tj) = OMC (tj) at the moment is recorded; according to a formula k = f'(t) = (OMC (tj)-OMC (ti))/(tj-ti), an oil mist concentration degradation slope k when the rotating speed and the oil supply quantity of the engine reach a preset interval twice is calculated; and whether the calculated k value is greater than a preset k value or not is calculated, and if so, an alarm is given. Visibly, the oil mist concentration degradation slope serves as the reference value of the alarm, the alarm is given before the oil mist concentration reaches theoil mist concentration alarm value, the health condition of the engine can be judged in advance, engine parts are prevented from losing efficacy, and potential safety hazards are checked in time.