Based on the re-examined precursory data of the Tangshan earthquake of July 28, 1976, the complexity and regularity shown by the pre-earthquake anomalies as well as the problems brought about to the practical prediction are analyzed. Three main points are discussed: 1) The diversity and three stages of the precursors of the Tangshan earthquake; 2) The synchronism as well as difference in time of the emergence and pattern changes of the precursors; 3) The relative concentration of the intermediate-term anomaly and the scattered distribution of the short-term and imminent anomalies in space. Furthermore, according to the research results achieved in recent years in China, the physical mechanisms of the precursors of the Tangshan earthquake are identified. The rock dilatancy of the focal body, aseismic fault creep, and mass movement are considered as the basic causes of the precursory complexity.