Combined structure of “largediameter high pressure jet grouting piles + doublerow borehole cast piles” is used as the retaining structure of a foundation pit in deep soft strata under complex construction environment. In the paper, the deformation of the support structure, the ground surface settlement and the plasticized zone and plastic strain of soils between the piles under different combined working conditions of jet grouting piles and borehole cast piles are analyzed by means of numerical calculation and site monitoring, so as to study the behavior of the combined support structure. Conclusions drawn are as follows: 1) The deformation of the foundation pit can be brought under effective control by adopting the combined support structure of “largediameter high pressure jet grouting piles + doublerow borehole cast piles”, however, the safety requirements of the foundation pit cannot be guaranteed by only adopting jet grouting piles or by only adopting doublerow borehole cast piles; 2) Compared to the number of the doublerow borehole cast piles, the parameters of the jet grouting piles have more impact on the behavior of the support structure. The paper can provide reference for the design and application of similar support structures in similar projects in the future.