High-purity magnesiumMagnesium is highly promising for medical implants due to its excellent biocompatibility, bio-functionality, and appropriate degradability. However, ingots produced by traditional casting methods usually have many pores with uneven sizes and non-uniform spatial distribution. These pores can compromise the performance and lifespan of the implants produced by such ingots. Here we propose a novel casting method based on layer-by-layer solidificationLayer-by-layer solidification through unidirectional heat dissipation. This approach changes traditional multidirectional solidification to unidirectional, reducing the generation of shrinkage holes. Additionally, thin-layer melts facilitate bubble escape and will limit the composition segregation and microstructureMicrostructure differences within the thin-layer range. Industrial CT and X-ray imaging revealed that the high-purity magnesiumMagnesium ingot produced by this method had no detected pores within the entire inspection range, with its quality surpassing the AAA standard grade. Composition analysis showed a great uniform distribution of 10 tested impurity elements along the length of the ~680 mm long ingot. This method is expected to provide high-quality materials for biodegradable magnesium implantsMagnesium implant, accelerating their entry into the medical market.