The results of and analysison the monitoring for the construction of a foundation pit of a shield machine launching shaft is presented in the paper. Monitoring is performed for the deformations of the diaphragm walls, the axial forces of the retaining structures, the ground surface subsidence, the ground deformations and the ground water levels, therefore the variations of the lateral displacement of the diaphragm walls and that of the ground occurring during the excavation of the foundation pits are obtained. On basis of the monitoring results, the installation sequence of the retaining structures is timely adjusted and temporary local supports are installed so as to bring the deformation of the diaphragm walls under effective control so that the stability of thefoundation pit can be guaranteed.