There are many researches about learning strategies of adolescent students and adult learners, but few on learning strategies of middle-aged learners. Through a case study, the paper finds out that middle-aged learners use six classes of learning strategies in a high frequency, especially cognitive strategies, meta-cognitive strategies and social strategies. But compensation strategies, memory strategies and affective strategies were used at a lower frequency. The factors of age and life experience as well as cultural background are of great significance for the choice of using certain learning strategies. The results of the study also show that SILL is of high reliability for the study on learning strategies of Chinese second language learners.