Aims <p>Environmental stresses can influence root mechanical strength, the impact of submersion of the water level fluctuation zone on the root mechanical strength of <i>Cynodon dactylon</i> was evaluated in this study.</p> Methods <p>Variations in the physicochemical properties (root weight density and root activity), mechanical strengths (tensile and pullout strength) and failure types of <i>C. dactylon</i> roots were investigated using a submersion experiment with 8 durations (0, 15, 30, 60, 90, 120, 150, 180 d), with a treatment without submersion serving as the control (CK). Additionally, corresponding variation in the microstructure of the roots was observed.</p> Results <p>The root weight density, root activity, root tensile strength and pullout strength of <i>C. dactylon</i> rapidly decreased, followed by a gradual decrease with increasing duration, and the reductions during the first 15 d of submersion accounted for 65.15%, 75.86%, 61.14% and 68.26% of the maximum reduction during the submersion process, respectively. Negative power function relationships were found between root mechanical strength and root diameter. Submersion increased the proportion of fracture failures during the pullout process. Moreover, the influence of submersion on root mechanical strength and failure type was regulated by a reduction in root activity.</p> Conclusions <p>Submersion deteriorates the mechanical properties of <i>C. dactylon</i> roots and alters their failure type.</p>