The invention discloses a city river channel dredging system. The city river channel dredging system includes a solid-liquid separation device. The solid-liquid separation device comprises a compression structure and a filtration structure. The compression structure comprises a piston. The piston and the filter structure are arranged in a sealed and matched mode. The piston reciprocates in the filtration structure linearly. The filtration structure comprises a first cavity body, a second cavity body and a third cavity body. The first cavity body, the second cavity body and the third cavity body are arranged in a spliced mode in the moving direction of the piston. According to the multi-joint splicing design of the first cavity body, the second cavity body and the third cavity body, the length can be adjusted dynamically according to the sewage and the silt content within the sewage, and washing after using can also be facilitated; and the polygonal piston drives the cavity bodies to transmit together while compressing the sewage, and it is ensured that water can be discharged efficiently in all directions of the side surface of the second cavity body.