The invention discloses a coal float-sink test device which comprises a framework, a base and a scraper. The base is connected with the bottom of the framework and is perpendicular to the framework, a tray is arranged on the base, is connected with a first motor by a transmission mechanism and can be driven by the first motor and the transmission mechanism to linearly reciprocate in the horizontal direction, and the first motor is fixed onto the base; magnetic poles are arranged on two sides of the tray, a float-sink tank is arranged on the tray and is filled with magnetic liquid, and a densitometer is arranged in the float-sink tank; an overflow port is arranged on the float-sink tank, and the scraper is positioned above the overflow port; the scraper is connected with second motors by a driving device and can be driven by a driving mechanism and the second motors to circularly move in the vertical direction, and the second motors are positioned inside the framework. The coal float-sink test device has the advantages that the problems of long consumed time, high manpower consumption and medicine consumption and the like of the traditional coal float-sink tests can be effectively solved, the coal float-sink test device is low in cost, simple in structure, easy and convenient to operate and high in work efficiency, and the like.