Inulin was separated by different sizes,then the influence of different treatment on preparing inulin gels with different average molecular weight by heating-cooling method was investigated.Ethanol was used in step-by-step separation to separate inulin into 9 grades.The separation was also identified by SephadexG-50 gel column.The average molecular weight of each grade was measured by viscometer.Molecular weight,temperature and concentration of the inulin on the gel formation were studied.The average molecular weight in each grade was the same.The larger the molecular weight was,the easier a gel formed.If it was less than a certain weight,gel could not be formed.With temperature increasing,the gel became more and more difficult to form.Too high or too low temperature had negative effects on gels' formation.When temperature gets to 70℃,the concentration for forming a gel became the least.With the increasing of concentration,the temperature range increased.The temperature range gets to the widest when inulin concentration was 35%.