Abstract This study investigated the influences of cement particle distribution on the hydration process of cement paste using three-dimensional computer simulation. The pre-hydrated models of cement paste were generated by using both the correlation function (CF) method based on SEM images and the random distribution (RD) method. The hydration process of cement paste was simulated using the model based on the CEMHYD3D. The RD method was simpler and required less time in generating a pre-hydrated model than the CF method. In addition, the simulation results of the RD method were similar to those of the CF method in the properties of cement paste using the cement 133 with water-to-cement ratio of 0.3. Although the simulation results of the RD method was in good agreement with those of the CF method, authors highly recommended that the cement particles larger than a critical diameter (13 µm) in the simulation contain multiple cement crystalline phases whereas the other ones smaller than the critical diameter should contain a single phase. The proposed RD method was validated by using the previously reported experimental results using ordinary Portland cement as well.