The invention discloses an unmanned aerial vehicle undercarriage folding/unfolding system and an unmanned aerial vehicle. The system comprises a foot stand mechanism, a controller and a driving device. The foot stand mechanism comprises a plurality of foot stands, the bottom end of each one of the foot stands is provided with a sensor unit, the sensor unit is used to send a grounding signal to the controller when detecting a collision, the controller is used to control the driving device according to the received grounding signal during the unmanned aerial vehicle landing so that the driving device drives the foot stand corresponding to the grounding signal to retract, and if it is detected that the amount of the received grounding signals and the amount of the foot stands satisfy the preset function relationship, the controller controls the driving device so that the driving device drives the foot stand which is in the state of retraction to stop retraction. According to the embodiments of the invention, the grounding signal of the foot stand during landing is acquired, retraction of the corresponding foot stand is controlled according to the grounding signal, and other foot stands are controlled to stop retraction when the grounding signal of the last foot stand is acquired so that when a landing process is finished, the unmanned aerial vehicle is in a horizontal state. Compared with the prior art, the system has the advantage of different landform adaptability.