For the trajectory planning problem in hypersonic glide vehicle, a differential flatness based three-degree-of-freedom trajectory generation approach is proposed. Based on the flatness analysis of the simplified longitudinal motion model, the reference longitudinal trajectory planning problem was mapped into the flat output space to improve the solving efficiency by eliminating the dynamical constraints and reducing the design dimension. Then the initial problem was transformed into a nonlinear programming problem utilizing global polynomial approximations to the flat outputs. To compensate for the effects of the earth rotation and external disturbances, a Proportion-Differentiation control based reference trajectory tracking controller was designed with good convergence capability. By integrating the lateral motion determined by the error corridor of heading angle based bank angle revision, the three-degree-of-freedom gliding trajectory was ultimately generated. Numerical simulations were conducted to validate the feasibility and effectiveness of the approach presented here.