Abstract: The Study of double planar grid retarding integral spectrometer for lowenergy electrons is described. The intrinsic energy resolution of double grid ismeasured by simulation of electron gun. The result shows that the resolution(FWHM) is about 2eV, which seems to be independent of the electron energy. Itis desirable to be used in the measurement of neutrino rest mass from tritiumbeta decay with an improved grid and a better geometric structure.