The invention relates to a system for detecting the concentration of dissolved gas in transformer oil. The detection system comprises an industrial personal computer, a signal generation module, a laser light source module, a six-core optical cable, a ceramic membrane tube, a microphone, a pre-amplification module and a signal acquisition module, gas molecules dissolved in transformer oil enter the ceramic membrane tube through micropores densely distributed in the ceramic membrane tube, and the separated gas molecules absorb laser energy in the ceramic membrane tube to generate a photoacoustic effect so as to measure the gas concentration. According to the invention, the ceramic membrane tube integrated with oil-gas separation and photoacoustic excitation functions is adopted, and a sensing system does not need an air pump and an air valve, so that the system structure is greatly simplified.