The fall armyworm (FAW) Spodoptera frugiperda has invaded Jiangxi Province, Southeast China for the past three years. Although the FAW displays a very wide host range, one of its main host plants in Jiangxi Province is still field corn. This study systematically investigated the effects of food plants (corn, peanut, soybean and sugarcane) on life-history traits of FAW and tested the leaf contents of the total flavonoids, reducing sugars, sucrose and C/N ratio. We found that the FAW fed on corn leaves showed significantly shorter larval and pupal development times, larger body weight, higher growth rate, lower weight loss, smaller SSD, shorter preoviposition period and higher fecundity than those fed on peanut, soybean and sugarcane leaves. The pupal development stage was significantly longer in males than females, showing a protogyny phenomenon. Food plants changed the relationships between larval development time and pupal weight and between fecundity and longevity. The corn leaves showed significantly higher contents of reducing sugars and sucrose, lower content of the total flavonoids, and a moderate C/N ratio, suggesting that the corn leaf tissues are more nutritive. These findings may help us to understand why the FAW mainly infests corn plants and may be critical for the development of strategies to predict infestation levels.