The grouting of water-rich karst macrovoid formation is a difficult problem in foundation treatment as the filling, seepage-proofing and reinforcement requirements are high. Commonly used mortar is of poor water-dilution resistance, while cement paste-slurry is of weak controllability and serious waste. In view of the respective advantages of paste-slurry and sand, a novel controllable cement-sand paste-slurry which is suitable for water-rich Karst macrovoid formation is proposed in this paper via long-term indoor test with large sample. Results demonstrate that the cement sand paste-slurry is of large viscosity and initial yield stress with the bleeding rate declining to 0%-3%, the minimum fluidity reaching 10-20 cm, and the setting time adjustable in 2-30 min. In the flow rate of 0.4-0.6 m/s, the slurry retention rate reaches 85% after water scouring and dilution, stone rate is nearly 100%, and the 28 d compressive strength reaches about 10 MPa. Moreover, the cost of the cement-sand paste-slurry slurry is equivalent to ordinary cement paste-slurry; the slurry also has social benefits such as environmental protection. Although cement-sand paste-slurry is the preferred material for the seepage-proofing and reinforcement of water-rich karst macrovoid formation, the pumpability should receive enough attention in practical engineering application.