Abstract Polycarboxylate (PCE) superplasticizers are the most important additive in concrete, which can effectively improve the workability of cement slurry. Different from the traditional regarding of PCEs as dispersants, here, we understand the PCEs as nano‐lubricants. By employing the molecular dynamics simulation, a sophisticated model was used to evaluate the interfacial friction between the C–S–H particles. The results reveal that the PCEs can reduce the interfacial friction between the C–S–H particles, and thus increase the fluidity of cement slurry. Further analyses infer the role of PCE segments in lubrication. The carboxylates on PCEs ensure the anchoring and hinder the separation of Ca ions. The side chains are used to lubricate the C–S–H surface, due to the weak adsorption between the side chains and the C–S–H surface. Predictably, this study not only provides a method to directly evaluate the performance of PCEs but also suggests new insights into the colloid dispersion of the low‐water content system.