The present disclosure relates to a vehicle defrosting and defogging area ratio testing method and device. The testing method includes the following steps that: when an air conditioner in a vehicle starts a defrosting and defogging mode, a defrosting and defogging trajectory chart on a windscreen which is obtained at a preset time point is drawn on test paper piece of which the shape is corresponding to the shape of the windscreen; first paper piece mass of paper occupied by a visible area in the test paper piece and second paper piece mass of paper occupied by a defrosting and defogging areain the test paper piece are obtained separately, wherein the defrosting and defogging area is corresponding to the defrosting and defogging trajectory chart in the visible area; and the defrosting anddefogging area ratio of the vehicle is calculated according to the first paper piece mass and the second paper piece mass. With the method and device of the invention adopted, a traditional grid counting calculation method can be replaced; the division of the defrosting and defogging trajectory chart into a plurality of grid patterns is not required, and therefore, the accuracy of testing is improved, and a problem that the test result of a defrosting and defogging system is not accurate enough can be solved.