This paper is concemed with the kinematic onolinearity measure of parallel kinematic ma-chine tool(PKM), which depends upon differential geometry curvature. The nonlinearity can be de-scrlbed by the crrve of the solution locs and the equal interval iput of joints mapping into inequable interval output of the end-effectors. Such curing and inequation can be measured by BW curvature. So the curvature can measure the nonlinearity of PKM indirectly. Then the distribution of BW curvature in the local area and the whole workspace are also discussed. An example of application to the interpola-tion accuracy analysis of PKM is given to illustrate the effectiveness of this approach.