The invention discloses a multi-source solid waste composite high-fluid backfill material, a preparation method and application thereof. The backfill material includes 950-1050 parts of muck, 40-60 parts of cement, 10-20 parts of superfine slag powder, 10-20 parts of fly ash, 20-30 parts of phosphogypsum, 7-15 parts of high-efficiency curing agent, water 275-525 parts; Among them, the high-efficiency curing agent includes 50-70 parts of sulfonated formaldehyde-acetone polycondensate, 20-30 parts of water glass, 10-20 parts of sodium lauryl sulfate, and 10-20 parts of water-soluble epoxy resin , 0-10 parts of sulfonated oil, 0-10 parts of sodium sulfate, 0-10 parts of polyacrylamide, water glass, water-soluble epoxy resin and polyacrylamide are calculated according to the active ingredients. The backfill material is self-compacting, has high strength and good durability, and has low requirements on muck and construction environment. It is suitable for the construction of foundations and foundation trenches, and has a high utilization rate of muck, low cost, and is environmentally friendly. It has broad application prospects. .