In view of the complex flow field structure of the rear intake system, it is necessary to clarify its influence on the double-sided composite impeller, so as to provide reference for the structural design of the rear intake system. Compared with the traditional straight rear inlet scheme, two radial rear inlet schemes, namely elliptical and symmetrical airfoil rear inlet schemes, were designed. Numerical simulation was used to analyze the influence of different rear inlet systems on the compression characteristics and flow field structure of double-sided composite impeller. The results show that compared with the straight type rear intake pipe, the elliptic type rear intake pipe and the symmetrical airfoil type rear intake pipe are slightly worse in compression performance, but there is no significant difference in flow range. At the same time, the radial inlet with elliptical rear inlet is better, which can match the compression characteristics of double-sided composite impeller and meet the needs of stable exhaust of tail nozzle. As the axial velocity at the blade root of the auxiliary impeller decreases, the pressure gradient increases and the separation vortex is generated, which affects the performance of the double-sided composite impeller. This paper extends the understanding of the influence mechanism of the rear intake system with radial intake on the double-sided composite impeller.