Abstract: To fully harness waste mucky soil with high moisture content and broaden its range of intensive utilization, a novel composite curing agent with low-content cement was developed. An environmentally friendly poured solidified mucky soil (PSMS) suitable for backfill engineering was prepared. The type of cement used in curing agent, the ratio of base materials, and the types of additives were selected. Flowability, bleeding rate, setting time, and unconfined compressive strength (UCS) were utilized as evaluation indicators to determine the optimal ratio of curing agents based on uniform design method. The mechanical behavior of PSMS was evaluated under varying mud moisture contents, curing agent contents, and organic matter contents. Furthermore, the solidification mechanism of PSMS was elucidated. The results show that high belite sulphoaluminate cement (HBSC) and sulfonated oil (SO) are the optimal cement and additive for preparing composite curing agent, respectively. When the mud moisture content is 85% and the curing agent content is 12%, the PSMS prepared using the recommended ratio of composite curing agent exhibits excellent performance. When the curing agent content is increased from 8% to 20%, the 28-day UCS of PSMS is improved by 2.29 MPa. The recommended curing agent content should not be less than 12%. During the formation of calcium silicate hydrate, calcium aluminate hydrate and ettringite, water is consumed and the reticular structure is formed by cementation, which promotes the formation of stable and dense microstructure in the PSMS.