In order to prevent shield malfunction and reduce construction risk, an oil online monitoring system for shield is developed through longterm research on detection data accumulation and operation status of the shield. By using the system, realtime monitoring and remote monitoring on viscosity, moisture and laser granularity of main bearing lubricating oil and hydraulic oil can be realized, and the analysis and judgment of the performance state for the shield can ensure the smooth construction of the shield. The system installed on the shield is tested, and the data collected by the system are basically consistent with the offline test data, with 3.62% of the maximum deviation for some data, which could reflect the real state of the shield operation; and the stability and accuracy of the data could meet the use requirements. The successful development of online monitoring system of shield oil is expected to lay a foundation for the automation, network and intelligence of the future shield management.