This article studies the principle of mirage formation in nonlinear index

gradient fluids. Based on Snell's law，the optical path model is established. On this basis，the

optical path and mirage imaging law are simu- lated with MATLAB. A solution with negative

exponential gradient of refractive index in the vertical direction is con- figured，and the actual

optical path is obtained by irradiating the solution with laser. The data points of optical path

are extracted by tracker software，and the data are analyzed by MATLAB. The experimental

optical path function and imaging position are consistent with the prediction results of Snell's

law. We also analyze the rationality of neg- lecting the secondary factors in the experiment，which

shows that Snell's law is reasonable The law explains the cor- rectness of mirage formation.