Abstract: With the continuous and high speed development of the urban construction in Ningbo city, the research on how to control the stability and deflection of deep excavations in an urban district of a soft clay region to avoid the settlement, cracking and destroy of neighboring facilities is quite necessary. Therefore, the available literatures about the theory, experiment and numerical modelling for deformation, control technique and control criterion of the deep foundation pit engineering are analyzed in this article firstly. Then, the Ningbo urban rail transit project construction is reconsidered, the deformation law for deep foundation pit engineering is investigated, and the characteristic of horizontal displacement and settlement of ground is obtained by the base of the monitoring data of 14 deep excavations. On the basis of deformation characteristic, the method of data mining is used to present the forewarning index for foundation pits monitoring, which can provides control criterion for deflection of deep excavations in the Ningbo soft clay region. Although, there is a great deal of practice on depth foundation pit engineering in Ningbo city, nevertheless, the theory of design, calculation method, research and development for technique and equipment are relative lagged. Thusly the results of this paper can present a basic criterion to protect the neighboring facilities in Ningbo area, and can present as an example for the other areas of soft clay.