Bank retreat is affected by the physical and mechanical properties of riverbank soil as a major factor. To research the influence of water content on the mechanical properties of riverbank soil of Jingjiang River reach, the composition and mechanical properties of soils on Jingjiang riverbank were examined in a holistic sense via data analysis, indoor test and theoretical analysis; moreover, the effect of water content variation on the shear strength indicators of cohesive soil on Jingjiang riverbank and further on the riverbank stability was quantified using measured data of 2016. Eight typical bank retreat sections were sampled in 2017. Results suggest that the soil composition in the Jingjiang River reach is characterized by a typical composite structure involving cohesive upper layer and non-cohesive lower layer. With the augment of water content, cohesion of soil increased first and then decreased, while internal friction angle reduced continuously. In general, higher content of cohesive particles leads to greater peak value of cohesion. In addition, the formulae between water content and shear strength indicators are given. The stability of riverbank in dry season is fairly good, larger than that in rising stage; but in flood season and recession stage, riverbank stability is undesirable.