The phenomenon of unsafety and fluctuations during the process of robots transporting people up and down stairs created some drawbacks in controlling the user’s sitting position. In practice, this phenomenon is caused by the seat position control mechanism not responding to environmental changes. This paper presents the method and algorithm for controlling seat position on a robot that transports people up and down linear stairs according to slope through a sliding mode controller and a Kalman filter. This method and algorithm are valuable for building a robot control program that adapts to the operating environment, ensuring stability and safety for users on the moving robot to avoid overturning when going up and down stairs on high-rise buildings. Some simulation results performed on specialized software show that the robot’s object position response follows the change in stair slope, and the system’s oscillation phenomenon is limited.