Aiming at the problems of weak driving ability and low torsional stiffness of a pneumatic flexible arm, a new type of pneumatic flexible arm is developed using three fan-shaped driving cavities and convex–concave nested constraint ring structure. A prototype was constructed, and a static model of the elongation and bending characteristics of the flexible arm was established. In addition, static experiments were conducted. Through the comparative analysis of experiment and theory, the results show that the experimental data are basically consistent with the theory, which verifies the correctness of the theoretical model. When the elongation was 0 mm and the three fan-shaped driving cavities were filled with the same air pressure of 0.25 MPa, the driving force was 2087.3N; when the three fan-shaped driving cavities were filled with the same air pressure of 0.11 MPa, the flexible arm reached a maximum elongation of 140 mm and elongation percentage of 61.9%. The proposed flexible arm could be controlled to bend in any direction in the range of 0°–360° and at any angle in the range of 0°–98° by adjusting the pressure of the three fan-shaped driving cavities. The flexible arm overcomes the shortcomings of the weak driving ability and anti-torsion ability of the flexible robot and has strong flexibility. It can be used in flexible robots in the fields of service, medical treatment, and rescue and other operations to provide greater power and reliable support for manipulators and other actuators.