The invention discloses a novel compositing agglomerant, and a riverway, lake in-situ dredging and ecological restoration technology. The novel compositing agglomerant comprises the following components in parts by weight: 70 to 90 parts of diatomite, 20 to 30 parts of aluminium potassium sulfate, 20 to 30 parts of sodium carbonate, 15 to 20 parts of an inorganic chelating agent, 15 to 20 parts of a buffering agent, 8 to 10 parts of an enzyme biological accelerator and 6 to 8 parts of a deodorizing agent. In-situ dredging is adopted, construction is directly conducted in the riverway or the lake, and sludge obtained after treatment does not need to be transported outwards and filled, so that a large amount of manpower and financial resources are saved, and secondary pollution is avoided; due to in-situ dredging, sludge residues at the bottoms of the river and the lake are eliminated maximally, and activation and recovery of soil family microbial culture in riverbed and lake base mud are benefited; the novel compositing agglomerant has the advantages of high agglutination and settling speed, low water content of the sludge and small occupied land during operation, and meets the requiremets of river and lake management, so that water quality is improved, the activity of the river and lake sludge is recovered gradually through management, the river and the lake recover the self-cleaning capability, and ecological balance is achieved.