The invention discloses an application of alkali-slag cement as a soft base treatment material. According to the application, the addition amount of an alkali excitant in terms of Na2O in the alkali-slag cement is 3-7% that of slag powder in mass percent, and the optimal mixing amount is about 5%. The proportion of neat paste, mortar or concrete for preparing the alkali-slag cement by blending isdetermined according to a process and test. According to the application provided by the invention, the alkali-slag cement is applied to cement rotating spraying piles, cement mixing piles, reinforcedbases of sleeve-valve-pipe grouting process, supporting engineering micro piles and the in-pipe grouting and shotcrete engineering of pipe sheds of tunnel engineering, so that the early strength canbe improved, the construction period can be saved, the influence of organic matter such as humic acid and the like in underground water (with slit oil) is avoided, and the quality is easy to guarantee; and when the alkali-slag cement is applied to the shotcrete engineering, a quick-setting agent can be eliminated, and the process is simplified. When the alkali-slag cement is used in the engineering, only cement in a conventional construction method is replaced, the construction equipment, measures and steps of the conventional construction method do not change, and the application is simple and convenient.