Solar storms in the ionosphere have a great impact on human's life. It's of great significance to find an effective way for
an accurate prediction of solar storms. In this paper, we present a method based on GUVI FUV day-glow imaging data to
derive O/N2, an environmental parameter used to forecast Space Weather. In the retrieval, we selected two channels of
the FUV wavelengths, OI135.6nm and LBH2. In accordance with the linear relationship between O/N2 and 135.6/LBH,
we proposed 135.6/LBH to describe O/N2. With the method described in this paper, the data of a 4-day solar storm,
October 1 to 4, 2002, have been processed. Subsequently, the obtained O/N2 maps were in good agreement with previous
results. It demonstrated the retrieval process we put up is efficient.