The spectral characteristics of bend fiber Bragg gratings (FBGs) are theoretically and experimentally investigated. A bend fiber chosen as the reference waveguide in coupled mode analysis, the analysis model for bend waveguides and the mode solvers for leaky are studied, and the quasi guided mode (actually leaky modes) in the bend fibers are successfully solved. The influence of photoelastic effects is also taken into account during the mode searching. The variations of the spectral characteristics of bend FBG are analyzed by using coupled mode theory.The variation of Bragg wavelength is coincident with that obtained by experimental measurements . It is shown that red shift of Bragg wavelength is at the order of 10-2 nm for a common single mode fiber based bend FBG with bend radius of 1.0 cm.