To calibrate quickly key parameters of a small angle neutron scattering spectrometer, such as selecting neutron wavelengths, wavelength resolution , and the Q resolution under a geometrical layout of the spectrometer, the experiment data of small angle neutron scattering for silver behenate powder were fitted. First, the geometrical layout of spectrometer was chosen including the size of circular source,sample apertures of the collimator, the source-to-sample distance and the sample-to-detector distance. Then, the spectra of small angle neutron scattering on silver behenate were obtained under four different revolving speeds of mechanical velocity selector. Finally, these experiment data were inversed and analyzed. Obtained results show that the velocity selector constant is 2 329.2 r·m-1·nm, correspondingly, four different selecting neutron wavelengths are 0.776、0.582、0.466、0.388 nm, respectively. The wavelength resolution of the velocity selector is 23.75% by fitting these experiment data and the spectrometer Q resolution curves can be obtained by using the chosen layout parameter and different rotating speeds. It concludes that the key parameters of small angle neutron scattering spectrometer can be achieved by using silver behenate, which supports the exact analysis and inversion for experiment data of small angle neutron scattering.