Based on the geometric boundary conditions of central line of the S-shaped intake, a polynomial construction method was put forward in order to extend the selection of central line. Depending on the different position of inflection point, 9 typical central lines were given, and the respective S-shaped intake geometric models were built up. The total pressure recovery, outlet dynamic pressure and index were calculated by solving the 3-D Navier-Stokes equations，and concluded the relationships between the position of S-shaped intake central line inflection point and the performance parameters.