Abstract: The special nature of the red sandstone directly affects the excavation method of the deep foundation pit and the selection of the support system and its mechanical properties.Based on the field monitoring and numerical simulation methods,the surrounding surface settlement,building settlement,horizontal displacement of pile body,vertical displacement of pile top and axial force of internal brace were analysed during deep foundation pit excavation,so as to study the mechanical properties of the deep foundation pit support system in the red sandstone area traversed by Lanzhou Metro.The results show that there is a limit to the range of influence of pit excavation on the surrounding surface settlement.Horizontal displacement of the pile body of the enclosing pile increases with the excavation depth of the foundation pit from an inclined shape to a parabolic shape in which the top and bottom of the pile are small and the middle is large,and the location of the maximum horizontal displacement gradually moves downward from the top of the pile.Due to the role of the steel brace pre-added axial force,the change rule of the two braces axial force with time are shown as a slow growth,rapid growth,tend to stabilise the three stages.The sum of the axial forces of the two braces is positively correlated with the change of horizontal displacement of the pile body of the enclosing pile.The deformation of each monitoring item is within the safety control range,indicating that the pile-braced support scheme for the deep foundation pit of Yanbei Road Station is reasonable and effective.The results of the study can provide guidance for subsequent metro construction in the same type of red sandstone strata.