The invention discloses a wheelchair capable of climbing stairs smoothly and running on flats. The wheelchair comprises a chair, a lifting device and a running part, wherein the running part is used for bearing the chair, the balance of the chair is kept under the action of the lifting device, the running part consists of a planetary wheel mechanism and a differential drive system, four working states of the wheelchair can be achieved through the combination of the planetary wheel mechanism and the differential drive system and the four working states comprise running on flats, turning on flats, stair descending and climbing and the shift between stairs and flats. The wheelchair is provided with two sets of drive mechanisms, an electric motor drives a central shaft through a straight-tooth cone gear, a planet carrier is driven through a clutch on the central shaft, and stretching and keeping of an impeller are achieved through transfer and linkage of the clutch and an arrester, i.e., differential and identical speed of the central shaft and the planet carrier. The wheelchair is adapted to prior stairs, runs stably and continuously, is good in bearing capacity and can run on flats. By the aid of the wheelchair, the living trip of the elderly and disabled persons is achieved.