A flexible locomotion system is proposed to improve the active locomotion ability of gastrointestinal microrobots in the minimally invasive diagnosis. The locomotion system simulating inchworm-like locomotion comprises a flexible locomotion mechanism and a drive mechanism. The flexible locomotion mechanism is mainly composed of radial balloon feet and an axial telescopic pushrod. In addition, a developed universal joint is used to join two cavities of the microrobot to improve its locomotion flexibility. The drive mechanism uses the nylon wires to actuate the bellows bump for the balloon feet and stimulate the telescopic pushrod for the microrobot to realize the flexible drive. The developed microrobot prototype shows its diameter in 12.2 mm, length in 78 mm and the weight in 14.8 g, and realizes the maximum clamping diameter of 20.2 mm and the maximum axial stroke of 16 mm. The experiments show that the wire drive mechanism can provide the maximum force of 067 N for the bellows bump and 065 N for the axial pushrod, respectively. The microrobot prototype can move in the rigid plexiglass tube with different angles, and the average speeds in the horizontal and vertical tubes are 0.38 mm/s and 0.25 mm/s, respectively. In addition, it can move in the curving plastic tube with a minimum curvature radius of 49.3 mm and present an effective locomotion in vitro intestinal tract. It can be seen that the flexible locomotion system provides an effective and safe locomotion case for gastrontestinal microrobots.