The invention relates to a trenching assembly of a chain type trencher. Trenching tooth sets are arranged on a cutter chain of the trenching assembly, the trenching tooth sets of different specifications can be conveniently replaced through a first mounting structure, then grooves of different specifications can be rapidly matched, after the trenching tooth sets are abraded, the trenching tooth sets only need to be detached and replaced with new trenching tooth sets, then the trenching tooth sets can be directly used, a chain mounting block does not need to be replaced, the construction cost is reduced, when trenching is carried out on soil with different hardness, different chain units are arranged, stress is more uniform, abrasion is smaller, efficiency is higher, and then the trenching assembly adapts to different land conditions. With adoption of a soil cleaning scraping plate device, accumulation of covering soil after trenching can be reduced, and the quality of a trench is improved; with adoption of a spiral soil discharging device, cut soil returning into the trench can be reduced, and the working efficiency and the quality of the trench are improved; meanwhile, dug soil is accumulated beside the trench through the spiral soil discharging device, and backfilling after construction is facilitated.