The sensing characteristics of long-period fiber grating (LPFG) resonance wavelength shift owing to transverse load are theoretically analyzed, by considering influential factors such as strain-optic effect and the change of wave guide structure. The characteristics include the resonant wavelength shift and the interval between two resonant sub-peaks (namely transmission sub-pits) split in LPFG spectrum. According to the analytical properties, the sensitivity coefficients of the resonant wavelength shifts and the sub-peak wavelength interval, which are due to transverse load for a long-period fiber grating in single-mode fiber, are numerically calculated. The simulation results show that the shift directions and sensitivity coefficients of resonant wavelengths are dependent on the polarizations of light source. The resonant wavelength of linear polarization source in the direction of forcing transverse load shifts to shorter wavelength (blue shift), and the resonant wavelength corresponding to the polarization in the orthogonal direction of forcing shifts to longer wavelength (red-shift). The shift ratio of resonant wavelength to longer wavelength is over 2 times larger than that to shorter wavelength. The birefringence caused by transverse load splits the resonant peak (transmission pit) into two resonant sub-peaks in LPFG spectrum. The sub-peak shifts and the interval between two resonant sub-peaks are well linear with the transverse load, which can be used for highly sensitive measurement or absolute measurement of transverse load. These conclusions are in good agreement with the published results of the transverse load experiments.