Abstract: To address the measurement error of structured light in line structures caused by high-temperature welding at the interface in the aerospace field under variable-temperature media, line structured light measurement experiments for geometric feature were designed. Through the analytical modeling of the thermal-induced refractive index field, the influence law of the refractive index gradient distribution on the optical path transmission was studied. An error compensation algorithm for large gradient temperature field line structured light measurement was proposed. A variable-temperature medium measurement experimental platform was built, and experimental verification was carried out. The experimental results show that the measurement deviation of line structured light caused by the temperature rise process of air medium increases nonlinearly, and the change trend is consistent with the theoretical analysis. The error calculation method can effectively predict the systematic error of the line structured light measurement system caused by the refractive index change of air medium at different temperatures.