For the biggest top steel ring, the sampling device characteristic seriously influences on precision sampling. The simulation model was built in AMESim and certificated by experiments. Through simulation, the external load and the car interior are important factors in speed stability. It derived the calculation formula on external load and compared with experimental results. Under the load limit, the velocity will stable with load change. Above the load limit, the velocity will fluctuate violently. An overweight car prolongs the starting time and aggravates the braking vibration. Under a reasonable design specification, 300kg is optimum. These conclusions had been applied in this newly designed device effectively.