The invention provides a controlled hydraulic steel support of a foundation pit and the application thereof, belonging to the field of construction engineering. The structure of the invention comprises a fixed end steel support, a flexible end steel support, a stopping device, an electric cabinet and a signal control cable; wherein, the fixed end steel support and the flexible end steel support are fixedly connected by a screw bolt as an integrated steel support, the stopping device is arranged between the fixed end steel support and a foundation pit enclosing purlin; wherein, the fixed end steel support is composed by a hydraulic oil cylinder, a spherical-hinge base, a seal cover, a route sensor, a connecting plate, a sealed oil tank, a supporting seat, a pressure sensor, an electric motor plus pump and a valve; the steel support device can compare the collected real-time information such as shaft force data, route change data and the like with support default value, the computer-controlled hydraulic system can realize the automatic adjustment and compensation of the support shaft force, and the support shaft force is adjusted according to the monitored results during construction to realize the requirements of controlling foundation pit deformation and guaranteeing safety during the foundation pit construction process. The controlled hydraulic steel support can be widely used for the pit protection during the foundation pit excavation process.