By introducing isosceles prism，ellipsometry technique is used to measure the complex refraction index. Based on the principle of Fresnel formula and ellipsometry，the relationship between ellipsometric parameters measured by the instrument and ellipsometry parameters of the prism-liquid interface is analyzed theoretically. The precision of measuring the refractive index and the absorption coefficient of the liquid is also discussed. The water and Indian ink are measured by the null ellipsometer，and the experimental curves of the refractive index，the absorption coefficient between the concentration of the samples are obtained. The experimental results are basically consistent with the references. The experimental results show that the accuracy of the prism ellipsometry technique　measuring the refractive index and absorption coefficient of the liquid are 0.0004 and 0.0003，respectively. The prism ellipsometry is suitable for rapid measurement.