In this paper, the robust stabilizer with Riccati equations is applied to vehicle longitudinal system design. In our design, even if the uncertainties exist in vehicle systems, the designed observer and state feedback controller can stabilize the systems for any given initial conditions. In this method, Riccati equations are solved for finding positive-definite symmetry matrices to construct the observer and state feedback gain matrices. After the inter loop is stable, the PI controller is designed in outer loop for improving the ability of tracking performance. Finally, the simulation shows the feasibility of our design.