Abstract: The calculation of the flexspline stress, which is based on the simplified theory of the column-shaped shell, is to some degree not very accurate. So the fracture of the ring gear in column-shaped flexspline in reality has always remained a pr- oblem hard to solve. The column-shaped flexspline at harmo- nic drive is taken as an example here, and a model imitation of the engaged flexspline is set up. A surface-to-surface contact element is set up between the nodes on the contact surface of the engaged gears. Applying the finite element calculation of 3-D elastic contact problems, a thorough calculative and analy- sis is done in terms of the stress and its distribution of the beari- ng flexspline ring gear and the column, of the deformation of the gears tooth and the effect. The main reason of the flexspline fracture in the design phase has been found out, and the positi- on possible dangerous section is predicted. According to the flexspline theory, a calculation with above result is conducted again the effect coefficient of the gear tooth is revised, and the flexspoine strength is double checked. In general compared the theoretical calculation to the actual fracture, a more close-to- the-reality result is reached, in addition, a more accurate, effici- ent method for solving flexspline problem is offered.

Key words: Contact problems, Column-shaped flexspline, Effect coefficient of gear tooth, Finite elements, Harmonic drive, Stress Strength