Semi-flexible pavement (SFP) combines the best features of both flexible asphalt and rigid cement concrete pavement. SFP consists of a porous asphalt mixture skeleton with 25 %–35 % voids, filled with selected cement slurry. To better balance the flexible and rigid characteristics between the asphalt mixture skeleton and hardened cement paste in SFP, a further understanding of its cement slurry formulation design is required. Results indicate that the penetrant has a significant effect on the fluidity of cement slurry, improving the flowability of cement slurry. Polycarboxylene-based superplasticizer is a desirable penetrant with the dosage of 1 % by mass of cement. Also, the optimum water–cement ratio of 0.6 for cement slurry is proposed, at which the fresh cement slurry can fully penetrate into asphalt mixture skeleton, and improve the engineering properties of SFP. Additionally, styrene butadiene rubber (SBR) latex is an effective flexible admixture for cement slurry, and its dosage of 2 % by mass of cement is proposed. SBR latex improves the stability of fresh cement slurry and enhances the flexibility of hardened cement paste to reduce the cracks in SFP. At the micro level, the fiber-like hydrated products between SBR latex and cement particles improve the flexibility of hardened cement paste. This reduces the cracks on the interface between asphalt mixture skeleton and hardened cement paste when the ambient temperature changes. It is concluded that chemical admixtures are essential requirements for the production of high performance cement slurry. They allow the fresh cement slurry to fully penetrate the asphalt mixture skeleton with a lower water–cement ratio, improving engineering properties of SFP. The proposed cement slurry formulation can better meet the requirements of mechanical properties and durability characteristics of SFP.