Based on ray trace method, Monte-Carlo method and Simplifie-Equation iterative method, the spectral transimttance radio calculation model for semitransparent liquid was developed and two inversion methods of optical constants (extinction coefficient k and refractive index n) of semitransparent liquid were analyzed. The application range of two inversion methods were investigated. The optical constants of Heptane attained in the references were selected as the true values, and the spectral transimttance radio of the semitransparent liquid based on the direct model simulation were regarded as the experimental values. The optical constants of Heptane were achieved by the inverse models. Then the influence of measurement error on the inverse results were also investigated. The results show that the standard deviation of k calculation error by the MC and SEI inversion methods are less than 10-6, while that of n are higher than 0.1％, and the influence of measurement error on the inverse results is urgent distinctness, and inversed calculation precision of optical constants becomes lower when the measurement error are higher.