In this paper, the construction of a shield tunnel crossing underneath existing Metro tunnel in Beijing is numerically simulated by means of FLAC3D software. Study and analysis are made on the construction of the shield tunnel; and then effective settlement control technologies are proposed. The results show that: 1) The modification of the construction schemes based on data measured can provide effective reference for the shield boring. 2) The settlement control effect can be improved by increasing the shield thrusting force and thrusting speed. 3) The polyurethane isolating ring and “clay short” can obviously improve the settlement control effect.