Different travelling mechanisms have different adaptability and passability in complex and unpredictableground environments.In this paper,by considering the advantages of wheel and track,a new wheel-track transformablewheel,which consists of a diameter-varying wheel rim as well as some track parts and changes its travellingmode according to the ground environment,is proposed.According to the ground environment,the transformablewheel can pass complex terrains either in wheel mode or in track mode without changing the driving mechanism,so that it is of excellent adaptability and passability.Moreover,it is designed in a modular mode and can bedirectly installed in vehicles,just like common inflatable tires.Analysis results of two locomotion modes show that,with the increase of the diameter-varying ratio,the track mode may result in stronger climbing ability and obstacleclimbingcapability than the wheel mode.