The invention discloses a floater stability measurement test device and method. A buoy is connected with a first counterweight vehicle, a second counterweight vehicle and a third counterweight vehiclethrough a first traction cable, a second traction cable and a third traction cable, the first counterweight vehicle applies a first pulling force to a bottom end of the buoy through the first traction cable, the second counterweight vehicle applies a second pulling force to a top end of the buoy through the second traction rope, a first pulling force direction and a second pulling force directionface two sides of an axis of the buoy respectively, the third counterweight vehicle applies a downward third pulling force to the bottom end of the buoy through the third traction cable, and the buoyis provided with an attitude measurement module used for measuring attitude information of the buoy located in water in real time. The stability test process of a floater under the action of externalforce is achieved through the cooperation of the counterweight vehicles and the buoy, and the stability curves of the buoys with different water discharge capacities can be obtained by controlling the counterweight vehicles to output corresponding tensile force.