The farfield beam patterns after the magnetic fluid sample are simulated. The scheme for realizing the thresholdtunable optical limiters is proposed. The relationship between the output power and the incident power at several different aperture radiuses and different distances between the aperture and the sample are investigated through theoretical calculations. The results show that the threshold value of the optical limiting system shifts to high power when the aperture radiuses are increased and the distances between the aperture and the sample are decreased. The linear relationship between the threshold value and the aperture radius is obtained. The threshold value of the optical limiting system decreases with the increase of the absolute value of the magnetic fluid characteristic parameter (f). The results presented in this work may be helpful for designing the magneticfluidbased thresholdtunable optical limiters.