An ultra-high-strength grouting material, designed for wind turbine foundations with a compressive strength exceeding 135 MPa, has been developed by mixing a polycarboxylate superplasticizer, defoamer, plastic expansive agent, and composite early strength agent. An systematic investigation has been made of the influence of these admixtures on the various properties of grouting materials. Results show that proper adjustment of admixture dosages enables a precise control of the flowability, strength, and expansion rate of the grouting material. Moderate addition of water reducing agents helps to improve the flowability and later strength of grouting materials. The addition of defoamers helps to optimize the material strength while affecting its flowability. Expansion agents help to improve the early shrinkage performance of materials with a potential influence on their later strength. Early strength agents help to significantly improve the early and later strength of materials while reducing their flowability. The comprehensive performance of the prepared grouting material is optimized when the dosage of water reducer is 0.6%, defoamer 0.3%, expansion agent 0.03%, and early strength agent 0.8%, with an initial fluidity of 312.5 mm, a 28 d compressive strength of 138.75 MPa, a 3 h expansion rate of 0.107%, and a 24 h-3 h expansion difference of 0.042%.