The invention discloses a riverway sewage sampler which comprises a central shaft. A counter weight body of which the outer diameter is greater than that of the central shaft is welded at the bottom of the central shaft; four surfaces of the central shaft are vertically welded with supporting plates; one or above of fixed shaft sleeve is welded at equal intervals on the lower end face of each supporting plate; a sampling ball is filled at the bottom of each fixed shaft sleeve; a protrusion is formed at the top of each sampling ball; each protrusion is disposed in a fixed hole formed on the lower end face of the corresponding fixed shaft sleeve. When the riverway sewage sampler is in use, each sampling ball is in a wizened state, the sampling balls are randomly thrown into a riverway and positions of the sampling balls are continuously changed along with riverway water, so that the riverway water at different positions can be absorbed one by one, thereby implementing sampling on the riverway water at different positions; sampling at the random position can be implemented without any electronic equipment.