•Properties of CSAB cement were investigated with different water and gypsum content.•Thermodynamic modeling based on QXRD results was conducted to explore the hydration.•Increasing water promoted hydration, but lowered the strength development of pastes.•Gypsum played a role in controlling the hydration of ye’elmite as well as belite.•Strätlingite formation depended on a water content and a kinetic effect of hydration. The main objective of this study was to investigate the phase and strength development of calcium sulfoaluminate-belite (CSAB) cement pastes with different amounts of gypsum and water. Thermodynamic modeling and a series of experiments including X-ray diffraction (XRD), thermogravimetric analysis, isothermal calorimetry, and compressive strength tests were performed. Decreasing the mixing water increased the strength of CSAB pastes, but decreased the degree of hydration. Interpretation of the early age XRD results and thermodynamic modeling suggested the formation of a meta-stable phase from the hydration of belite, possibly C-(A)-S-H, which transformed into strätlingite at later ages only in the samples with high water content, likely due to easier diffusion of ions at higher w/c. Furthermore, the XRD results and thermodynamic modeling confirmed that the amount of gypsum controls the hydration of ye’elimite as well as belite in the CSAB cements.