The present disclosure provides a performance testing method and system for a polycarboxylate superplasticizer in a concrete system. An interface model is constructed based on a calcium silicate hydrate (C—S—H) gel model and a molecular dynamics model of a polycarboxylate superplasticizer, which can cover complexity of a cement particle interface and variability of the polycarboxylate superplasticizer, and can also establish a link between a microstructure of the polycarboxylate superplasticizer and a macroscopic fluidity of a cement across multiple scales. Meanwhile, friction resistance is accurately calculated based on the constructed interface model to accurately test a performance of the polycarboxylate superplasticizer, thereby shortening a screening cycle of the polycarboxylate superplasticizer and improving a performance optimization efficiency.