Fructooligosaccharides (FOSs), as a mixture of 1-kestose, nystose, and 1F-fructofuranosylnystose oligosaccharides, exhibit lots of beneficial effects on our health and have been used as food ingredients. There have been a lot of reports on how to raise FOSs yield in different ways, but almost nobody did any deeply studies on the composition of FOSs—proportion of each component. However, different components may have different functions and some even show side-effects. In this research, we employed immobilized fructosyltransferase to produce FOSs and got a maximum yield of 56.12 %. Then we successfully produced FOSs of different components proportions by adjusting the reaction parameters—pH, temperature, and fermentation time. We designed six groups to investigate the relationship between reaction parameters and components proportions, and the results showed that pH condition mainly affects the yield while reaction time mainly affects components proportions. It is the first time that the components proportions of FOSs are systemically investigated, and we finally figured out six protocols for producing different FOSs. This is a basic investigation on the relationship between FOSs components proportions and reaction conditions. We hope this research can be helpful for other researchers who are interested in this area.