[Aim]  To clarify the mechanism by which plant endophytes deter the herbivorous insect Rhopalosiphum maidis, and thereby provide a theoretical basis for the application of endophytes in the field. [Methods]  The effect of the plant endophyte Alternaria GX5 on various maize nutrients, secondary metabolites and hormones was investigated, and the developmental period, fecundity, and survival rate of R. maidis populations feeding on maize plants with, and without, the GX5 endophyte, were measured. [Results]  The GX5 endophyte significantly extended the developmental time of R. maidis by 10.02% (P=0.003), and significantly reduced its fecundity (P<0.001) and survival rate (P<0.001), by 43.55% and 46.72%, respectively. The endophyte also significantly increased the fresh weight (P<0.001), soluble sugar (P<0.001), tannin (P=0.029), total phenol (P=0.005), and salicylic acid (SA) (P<0.001) content of maize plants by 21.32%, 48.36%, 9.81%, 2.86%, and 14.41%, respectively. However, it significantly reduced their jasmonic acid (JA) (P<0.001) content by 22.47%. [Conclusion]  The GX5 endophyte significantly increased the amount of soluble sugar and secondary metabolites in maize plants, activated SA content, and inhibited JA content, thereby significantly suppressing the growth, development, fecundity and survival of R. maidis feeding on these plants. This study is of great significance for understanding the interaction among plant endophytes, plants, and herbivorous insects and provide a theoretical basis for the rational use of plant endophytes in pest control.