The causes of water inflow and sand bursting on starting shaft disaster in shield tunnel were analyzed. The analytical model that groundwater seepage from substratum of the reinforced soil to gap in shaft wall on starting shaft in shield tunnelling was established. Using the semi-confined aquifer seepage theory, a practical calculation example was given. The result shows: under the assumption that the reinforced soil was complete exclusion of water, the accidents of water inflow and sand bursting in portal part were influenced by many factors including the length of reinforced soil, groundwater level and so on. The cost and safety of starting shaft engineering had positive correlation with the length of reinforced soil. Lowering the groundwater can significantly reduce water inflow disaster. Comprehensively considered factors of safety, economy, construction period and so on, the reasonable construction parameters can be determined.