The article reviews the research results of influence of a complex modifying agent on rheological properties of cement-water paste and cement stone strength. The article describes the processes of hydration and structure formation of cement stone, the special aspects of the phase constitution of Portland cement hydration products in the process of modifying by complex admixture. The behavior of cement hydration in composition with the complex modifying agent have been shown by means of measuring the hydrogen-ion concentration, by sedimentation, contraction and heat emission of cement suspension. There is the decreasing of the degree of cement stone hydration because of blocking action of the superplasticizing admix and hydrophobisator during the initial stage. Studying the cement stone spalls with the aid of electron microscopy has showed that there are the crystallized hydrated newgrowths with smaller dispersive capacity in composition with the complex modifying agent than the ones without introduction of admixtures. The increasing of concentration of hydrated calcium sulfoaluminate in pores and capillaries, the increasing of the specific surface area of hydrated phases both in the general structure of cement stone and in structure with regions of imperfections, the voids content decreasing lead to the material hardening. The way of cement stone structure formation in composition with the complex modifying agent is found by means of differential thermal and X-ray phase analyses. This way is shown in the composition with a complex modifying agent manifested in blocking effect SP and HP, resulting in a reduced amount of portlandite and high content of the starting phase the cement clinker, wherein the MTK is reacted with calcium hydroxide, which helps to seal material. Reduction of ettringite in the composition with a complex modifying agent is associated with precipitation of superplasticizing admix molecules on C3A particles, which limits interaction with water.