Abstract: Hexagonal Diamond-HD (also known as Lonsdaleite) is a natural mineral found in meteorites that has attracted attention due to its unique structure and properties. Professors Bingbing Liu and Mingguang Yao from Jilin University, and Shengcai Zhu from Sun Yat-sen University, collaborated to innovatively propose the "Post-Graphite Phase Gradient Conversion method (PGPC)". This method enabled the first successful synthesis and preparation of high-purity (>95%) millimeter-sized Hexagonal Diamond-HD bulk, resolving a half-century-long challenge in this field. The Hexagonal Diamond-HD synthesized via the PGPC method exhibits excellent properties, making it highly promising for applications in ultra-precision machining, quantum information, and deep-space exploration. However, the expensive and complex equipment required, coupled with relatively small single-crystal sizes, may pose substantial challenges on the path to industrialization. Looking ahead, if the pressure window can be optimized and CVD epitaxial technology can be developed, the Hexagonal Diamond-HD could be product in large-scale industrially, thereby driving advancements in high-end manufacturing, quantum technology, and other related fields.