In order to study effect of the metal coating on the macrobending loss properties of a fiber loop, two mathematical models of the thermal stress and the associated photoelastic effect of the metal coated fiber loop are established. The thermal stress coefficients and thermal stress dependent refractive index coefficients of the fiber loop with metal coating are calculated. Impact factors of the thermal stress coefficients Kθt, Krt and the thermal stress dependent refractive index coefficient Kn are simulated. The results indicate that Kθt is much greater than Krt at the same circumstance. Consequently, the metal coated fiber loop mainly suffers the annular thermal stress and the radial thermal stress can be ignored. The thermal stress and its induced refractive index change alter with the reference radial position and thickness of the coating rather than the bend radius of the loop. When the thickness of the metal coating increases from 0 to 2000 μm, Kθt and Kn both undergo a process of a sharp increase, and than transfer to a slow growth and tend to a stable value. Since Kn is negative, refractive index decreases as the temperature increases. The presented models are feasible to explain that refractive index of the fiber decreases with the increase of temperature, thus altering the macrobending loss of the metal coated fiber loop.