The invention discloses a control method and device for the ratio of dual fuel of an engine, and a car. The control method comprises the steps that if the engine is in a rapidly accelerated state, thefirst demand quantity of the first fuel and the second demand quantity of the second fuel are calculated at the first position before top dead center of each air cylinder, and according to the calculated first demand quantity, a first fuel spraying device is controlled to spray the first fuel to all the air cylinders; and the third demand quantity of the second fuel is calculated at the second position before top dead center of each air cylinder, the second demand quantity of the second fuel is updated according to the third demand quantity, a second fuel spraying device is controlled to spray the second fuel to all the air cylinders according to the third demand quantity, thus when first fuel spraying lags and the first fuel actually sprayed into the air cylinders is excessively less, the ratio of the two kinds of fuel entering the air cylinders of the engine can be controlled and adjusted by increasing the spraying quantity of the second fuel, and the problem of insufficient car power caused by lagging of methane spraying-in under the suddenly-accelerated working condition of the car is avoided.