A drainer basket assembling structure of a stepping wringer bucket includes a bucket body, having a containing space concavely formed at the bottom of a front side, a shaft base formed at the top of the containing space; a base, having two support stands installed in the containing space; a driving mechanism installed between the two support stands for producing a driving force; a transmission shaft installed in the containing space and whose bottom is driven by the driving mechanism; and a drainer basket driven by the transmission shaft. An upper end of the transmission shaft is protruded out from the shaft base, and a protruding end is provided for sheathing the coupling base of the drainer basket and form a sheathing and linking structure with the protruding end of the transmission shaft, such that the drainer basket can be assembled from the top of the bucket body.