External sulfate attack is one of the situations that may cause gradual but severe damage in cementitious materials, which may lead to cracking, increased permeability and strength loss. In this paper, thin-walled hollow cement paste cylinders with a wall thickness of 2.5mm were made considering the slow penetration process of sulfate ions under continuous immersion condition. Three types of longitudinal restraints were applied on the hollow cement paste cylinders by means of a spring and steel bars through the specimens in order to facilitate non-, low- and high-restraint conditions. Strain gauges were glued on the steel bars so as to increase the accuracy of the measurements. During the immersion tests, specimen expansion and generated stress were monitored. Additionally, sulfur element mapping was generated by EDS (energy dispersive X-ray spectrometry). Expansion behaviours of the hollow cement paste cylinders were simulated under the aforementioned restraint conditions which were carried out based on the Delft lattice fracture model. The expansion was assumed to be realized upon formation of ettringite inside the nanopores of the cement hydration products. Local expansion stresses were computed by employing the crystallization pressure theory. A comparison between the simulation and the experimental results showed reasonable correlation and tendency for further exploration of our approach. @en