The features of expanding cement strength and structure formation at different constrained deformation conditions were studied (without constraint of deformations, uniaxial constraint of deformations, biaxial constraint of deformations, and triaxial constraint of deformations). The study was conducted for three doses of 5 %, 15 % and 25 % of expander on the calcium sulfoaluminate basis in Portland cement of CEM 42.5 mark. For experimental data interpretation in the analysis of structure and phase composition, the combination of methods of x-ray diffraction, differential scanning calorimetry and scanning electron microscopy were used. The constraint of expansion deformations has a significant impact on the volume and nature of the expanding cement pore structure, and leads to the formation in the volume of cement stones of black agglomerates, which represent the mixture of portlandite and ettringite crystals, uniformly distributed in the amorphous CSH-phase. It has been established that by increasing the expander amount and the degree of deformation constraint increases the number of black agglomerates and an increase in compressive strength.