Abstract: With respect to the characteristics of the special soft-soil along an expressway in northern Jiangsu province, the CMSC firming agent was synthesized with ingredient method of full powder by adopting two projects and added into soil with given proportion. Meanwhile, considering the local hydrologic and climatic factors and aiming at the conservative soaking condition, a new hit canister was invented. The soils improved with the CMSC firming agent were compacted in the new hit canister. The compacted samples were taken out and cured. When the curing time was mature, they should be soaked into the water with the new soaking equipment. At last, the pluging test was conducted. It indicated that the compacted samples were saturated within three-dimensional soaking condition. The CBR value was ensured its credibility within this new soaking condition which was closer to the actual situation. The engineering properties of soil improved with CMSC firming agent were better than lime-improved soil. The optimum proportion of CMSC firming agent could be obtained and the improving mechanism of CMSC soil firming agent were studied further more. The results could be used for reference to further study and engineering application.