Two methods were proposed to deduce the distribution of the Fraunhofer diffraction field for one dimensional Variable-Line Space gratings(VLS gratings), including surposing the complex amplitude of the diffracted light by a narrow slit and strict integration of illustrating area of grating depended on the scalar theo-ry.It shows that both calculating results are nearly the same when the grating has similar slit widths of different periods.But when the VLS grating has variable slit widths, it represents obviously difference with the position and intensity of higher diffraction orders except the zero order.Examples are taken to analyze the distribution of diffraction field of VLS grating, which are also discussed by simulating with Matlab software.From the preced-ing discussion we can immediately draw a conclusion that strict integration depended on the scalar theory is more suitable for VLS grating to investigate its diffraction field distribution.Moreover, brief introduction was given about the ability of VLS gratings for displacement sensor and focusing wave, basing on the above analysis.