Geometrical nonlinearity of a fine objective lens′ bellows actuator was analyzed with finite element method, and characteristics of bellows actuator were evaluated by linearity. Geometric nonlinear deformations of some common bellows(U shape, S shape, C shape, rectangle shape and triangle shape) were analyzed via the finite element method, the stoke and linearity of these actuators were obtain with the least square method. The results show that: the S shaped bellows, of which linearity is up to 0.161%, is the best one for large stoke bellows actuator, and the triangle shaped bellows, of which linearity is up to 0.135%, is the best one for small stoke bellows actuator.