Small angle neutron scattering (SANS) technique is a powerful tool for nanometer structural analysis of materials. The process of SANS measurement

and the raw data reduction

is relatively complicated. In order to obtain the absolute SANS intensity

one needs to measure intensities of the incident and scattered beams

the sample transmission

the background

the scattering and transmission of the empty cell etc. If a wide scattering vector range is needed

one has to measure the same sample under different instrument configurations. Also

a large number of data treatments are needed before one obtains the SANS data for further analysis. In this paper

after a short introduction to the SANS basic theory and the experimental system

we focus on the raw data reduction method

in which the averaging and the combination of the isotropically scattered data are discussed in detail.