Aiming at the problem of measuring the optical signals of partial discharge inside the transformers, this paper studies the attenuation characteristics of partial discharge optical signals in transformers and establishes a transformer oil discharge optical signal detection system based on fluorescent optical fibers. The optical signal characteristics and optical electrical signal relationships during corona discharge, spark discharge, and arc discharge stages in oil are studied. The experimental results show that the intensity of optical signals in oil decays approximately exponentially with increasing propagation distance, and the attenuation of optical signals in the infrared band is higher than that in the visible and ultraviolet bands. There is a good relationship between the discharge optical signal and the pulse current signal, which is approximately linear. There are significant differences in the radiation intensity of the optical signal at different discharge stages in oil.