Abstract: In order to ensure the construction safety of shield tunnel undercrossing isolated shallow foundation railway bridge in water-rich sand stratum, taking Nanchang Metro Line 4 undercrossing Qingshan Road overpass of Bei?jing-Kowloon Railway as the engineering background, the reinforcement measures of stratum grouting and cast-inplace raft foundation frame culvert are put forward by means of construction method comparison, numerical analysis and field monitoring. The law of track settlement is analyzed, and the effectiveness of reinforcement measures is verified. The results show that it is reasonable and effective to use stratum grouting and cast-in-place raft foundation frame culvert to reinforce the railway bridge and realize the control of track settlement before shield tunnelling. Compared with the condition without any reinforcement measures, the maximum value of track settlement is reduced by 83.53%, which is 1.88 mm. The field monitoring results show that the maximum settlement of the track is 1.45 mm after stratum grouting and cast-in-place raft foundation frame culvert reinforcement, which verifies the correctness of the numerical analysis results and the effectiveness of the reinforcement measures, and ensures the normal operation of the Beijing-Kowloon Railway.