The embodiment of the invention provides a method and device for determining the size and quantity of bubbles in foaming oil. The method comprises the steps that firstly, a first CT scanning image of a first rock core obtained after being dried with wash oil is obtained; a second CT scanning image of a second rock core in the first pressure state is obtained; a third CT scanning image of the second rock core in the second pressure state is obtained; according to the first CT scanning image, the second CT scanning image and the third CT scanning image, the size and quantity of the bubbles in the foaming oil are determined when the pressure in the second rock core is the second preset pressure. By means of the method and device for determining the size and quantity of the bubbles in the foaming oil, the size and quantity of the bubbles in the foaming oil can be more accurately determined.