Lightweight aggregate concrete is widely used to strengthen existing normal concrete structures owing to its lightweight and high strength. However, sulfate erosion has been shown to degrade LWAC-NC interface performance, posing a technical challenge for the composite systems after strengthening. To reveal the performance evolution of the LWAC-NC interface under sulfate environment, splitting tensile tests were conducted to analyze the bond strength of the interface after sulfate erosion at various mass fractions (0, 3%, 5%, and 7%). The results revealed that with increasing erosion duration, the interfacial eroded area and microporosity increased. The interfacial splitting tensile strength and fracture energy increased before declining. After 150 days of exposure, strength decreased by 9.0% to 28.1% and fracture energy by 5.3% to 35.8%. Entropy-based analysis further revealed that sulfates affected interfacial fracture energy more than interfacial strength. Additionally, an evolution model for interfacial splitting strength was developed incorporating concrete strength, interfacial roughness, pouring time differences, sulfate concentration, and erosion duration. The model error ranged from -19.3% to 19.6%, which is intended to provide the reference for the application of LWAC(lightweight aggregate concrete) in sulfate-rich environments.