In order to study the unconfined compressive strength of lime-improved red clay and its influencing factors, combining with the engineering practice, investigated the effective aspects of lime content, compactness, curing conditions, water content and particle size in unconfined compressive strength tests. Meanwhile analysed the factors’ prominent property by the method of nonrepeative double factors variance analysis. The analysis results showed that compactness and curing conditions were the main influence factors of unconfined compressive strength, and lime content, water content and particle size were the secondary influence factors. To meet the red clay subgrade filling requirements, on the condition of best lime content the compactness of subgrade should be controlled strictly, and the particle size, curing of the subgrade and water content should also be controlled.