The sensing principle of Fiber Bragg Grating (FBG) temperature sensor is briefly introduced. Using the sensitivity of FBG sensing technology to temperature change, FBG sensor is applied in the leakage monitoring of the mechanical pipeline connection. By measuring the temperature difference at the leakage, the connection state of the pipeline connection system is analyzed, and the test is designed to explore its feasibility and influencing factors. The results show that: this method can respond to the change of temperature in a short time, so as to effectively warn the leakage, the stable temperature difference of 1.81 ℃ can be measured in the windless environment, which shows that the method is feasible; the two factors of wind speed and water temperature can affect the stable temperature difference, so this method is of better leakage monitoring effect when the wind speed is large and the difference between water temperature and ambient temperature is large.