To address the surface distresses such as surface polishing, aggregate exposure, pitting, and unevenness in cement concrete pavement, a polymer composite modified cement mortar material incorporating both polypropylene fibers and redispersible latex powders was designed for the bonded thin overlay repair of existing cement concrete pavement. Based on the orthogonal test method, composite modified mortars with different mix proportions were prepared, and their performance indexes, including fluidity, flexural strength, compressive strength, and drying shrinkage, were tested to optimize and determine the optimal mix proportion. The corresponding workability, mechanical, bonding, and durability properties, as well as the microscopic characteristics, were verified and analyzed. The results show that the composite modified mortar under the optimal mix proportion is a high-strength and low-modulus cement-based composite material; its strength exceeds the technical requirements of C40 concrete for cement concrete pavement, and it has good workability, volume stability, impermeability, and impact resistance, along with strong bonding performance with concrete. Polypropylene fibers enable hydration products to form a dense microstructure, and redispersible latex powders construct a network membrane structure to fill the microscopic pores of the mortar, thereby enhancing the interface bonding strength and matrix impermeability. The various performances of the composite modified mortar meet the performance requirements for bonded thin overlays of cement concrete pavement.