The invention discloses a method for detecting settling velocities of suspended sediment groups. The method includes reducing a diffusion equation under hypothetic conditions of constant states and zero concentration gradients of water flow directions; performing hypothesis according to a sediment diffusion theory; acquiring instantaneous velocities and instantaneous sediment concentration synchronous with the velocities by the aid of an ADV (acoustic Doppler velocimeter); finally acquiring the settling velocities of the suspended sediment groups. The method has the advantages that the method is applicable to laboratories and fields, and can be applied to fine-grained suspended loads no matter whether flocculation actually occurs or not, distribution of the settling velocities along the depth of water and change of the settling velocities along with the sediment concentration can be measured by the method, and an effect of the method is superior to an effect of the traditional measuring method.