Torsion stiffness of air spring, the important parameter of influencing railway vehicle curve-passing performance, wasresearched. The structure principle of air spring was introduced, and an air spring torsion test bench was designed. Based on the testbench, the influence of the conditions of different torsion vibration amplitude under the same vertical load and the same torsion angleunder different load on air spring torsion stiffness was studied. The results showed that: under the same vertical load, torsion stiffness wasdecreasing with the torsion vibration amplitude increasing, while, under the same torsion angle, torsion stiffness was increasing with thevertical load increasing. The research results provided the reference for air spring development and experiment.