In many rescue and detection tasks, mobile robots are required to transverse over uneven terrains and enter some dangerous environments that people cannot overcome, such as crevices, pipes, gullies, etc. High mobility/speed and adaptability to complex environment are two important performance indexes for mobile robots. Legged robots are with high environmental adaptability, while wheeled robots are with high mobility. Since existing mobile robots cannot meet these two requirements simultaneously, a flexible, extensible, and reconfigurable multi-terrain vehicle with a varying wheelbase is proposed innovatively. The vehicle body contains two main parts: one middle plate and two side plates, which both have two active wheels and are connected to the same shaft, which has two passive wheels on both sides. Specially, the included angle between one middle plate and two side plates is driven by an active motor, and then the vehicle can behave many forms by adjusting the wheelbase between two pair of active wheels. Under the body configuration, the multi-terrain vehicle can achieve the motions of crossing deep pit, climbing stair, crossing height limiting rod, climbing crevice, and crossing pipe by folding and varying the wheelbase. First, the detailed mechanical structure of multi-terrain vehicle is designed. Second, the kinematics of the multi-terrain vehicle including the inverse and forward solutions of wheelbase and centroid velocity are analyzed. Third, the control scheme combining travel speed controller, turn controller, and wheelbase controller is proposed based on proportional-Integral-derivative algorithm. Finally, many simulations and experiments validate both the feasibility and effectiveness of the proposed structure and control of the multi-terrain vehicle.