Fata Morgana phenomena are usually presented in the vertical direction with more than three mirages at the same time, which are upright or inverted, alternating tensed and compressed, and distorted. In this paper, the complex optical phenomenon is reproduced by physical experiment and the variation of mirage with observation distance is explored. Then the variation law of mirage is analyzed quantitatively by numerical simulation. The results show that the number, position and shape of the mirage vary with the distance of observer, gradient of refractive index and thickness of the medium. The compression ratio and initial distance of the inverted mirage are positively and negatively correlating with the gradient of the medium respectively, while the distance between upright mirage and inverted mirage is negatively correlating with the thickness of the medium.