The present invention relates to a test method for porosity of an asphalt mixture, and an apparatus thereof. With the present invention, the volumes of the pore with an opening and the pore with a semi-opening can be determined. The test apparatus mainly comprises a sealed container, a pressurization device of the sealed container, a hydraulic cylinder, a water pump and a flow control valve. The sealed container is provided with a pressurization piston. A piston rod of the hydraulic cylinder is connected with the pressurization piston arranged inside the sealed container. The flow control valve is connected between a water inlet of the sealed container and the water pump. The test method comprises that: a specimen is sealed with a thin film, and is placed in the sealed container; with thehydraulic cylinder, the piston inside the container is pushed, such that the air pressure in the container is increased to more than two standard atmospheric pressures; water is slowly injected to the container until the height of the water is the preset height, and the water injecting amount is recorded as L1; the specimen is taken, and the thin film is removed, then the specimen is placed in the container again; under the same air pressure condition, water is slowly injected in the container, and the water injecting amount is recorded as L2; the difference between the two water injecting amount is the amount that the water enters the inner pores of the specimen, and the porosity of the specimen can be calculated, wherein the difference is calculated by the following formula, L2-L1.