To measure the Refractive Index (RI) of transparent liquid and translucence liquid in industrial process in real-time, in situ and non-contact, a simple method for measuring liquid RI was proposed based on the optical property of glass pipe wall is presented in this paper. By coating a transmission-scattering layer on the outer wall surface of a glass pipe, the incident laser beam was transformed into a wide-angle distributed transmitted scattering light in the glass wall. After the scattered light reached the interface between the pipe wall and the liquid, the scattered light satisfying the condition of total internal reflection was reflected to the transmission-scattering layer to form automatically an oval dark pattern related to the RI of the liquid in the pipe. The method to measure the RI of the liquid in the glass pipe in situ and non-contact could be implemented according to the analytic relation between the long axis length of the oval dark pattern and the liquid RI in the glass pipe. Several RIs of transparent liquid and translucency liquid were measured. The experimental results show that the accuracy of this apparatus is the same as that of an Abbe refractometer(±2×10-4 RIU(refractive index unit)). It concludes that the method is characterized by simple configuration, lower cost, anti-interference and higher robustness. It is suitable for the optical images relative to liquid refractive indexes, and is expected to monitor the liquid RIs of a closed pipe at an abnormal temperature and an abnormal pressure in real-time, in situ and non-contact.