To measure the angle shift that occurs under high-temperature conditions, a fiber-based high-temperature-resistant incremental encoder was developed in this study. First, a high-temperature-resistant fiber was employed to transfer light under high-temperature conditions. A field programmable gate array was used to process the incremental encoder's electric signal, and a USB was used to transfer the angle in a normal temperature environment. Second, the effect of the collimation degree of a light beam on the performance of the optical encoder was analyzed, and then a light-emitting diode (LED) convex lens fiber couple was developed. Finally, 23 surface polyhedrons and autocollimations were used to test the accuracy, and the accuracies of the LED convex lens fiber couple and fiber direct couple were compared. The results show that this system can work normally in 100 ℃ conditions. The size of the encoder head is 62 mm× 42 mm, the resolution is 0.3", and the precision 3σ is 13.55 ″, which represent an improvement of 20.8% over that of the fiber direct couple. The system thus satisfies high-temperature conditions.