To improve the quality of underwater excavation operations, this paper proposes a digital twin-based method for intelligent guidance and operational quality control of underwater excavation. By developing intelligent guidance hardware for the excavator and establishing the geometric relationships and kinematic equations of its components, efficient calculation of the bucket tip pose is achieved. A building information model (BIM) of the underwater excavation profile is established using Three.js and Unity 3D, and a digital twin model of the excavator is constructed by integrating real-time sensor data. Finally, based on real-time calculation of the relative distance between the bucket tip and the target excavation surface, an intelligent guidance and operational quality control strategy for excavation operations is developed, and the corresponding system is implemented. Case study results demonstrate that this method enables three-dimensional visualization of the excavation process and remote collaborative monitoring, provides intelligent guidance for operators to correct deviations, and ensures the quality of underwater excavation.