The basic linear tuning principle of fiber grating wavelength without chirp effect using variational section beam with uniform intensity is theoretically analyzed in this paper. Three kinds of basic design scheme of variational section beam and the condition that the elastic beam section as tuning device of the wavelength of fiber grating without chirp effect must satisfy are presented. The characteristics of the tuning technologies using cantilever beam based on identical section and variational section are discussed. It is shown that by bring lateral load to bear on simple beam and cantilever beam a linear tuning of fiber gating wavelength without chirp effect can be realized,and the setup is simple in structure and easy to design.