The crowned tooth gear coupling is a key component in modern heavy-duty shaft transmission; its crowned tooth meshing compensates angular, radial and axial misalignment between shafts. In China, the GICL, NGCL and GCLD series under GB/T standards are mainstream and widely used in metallurgy, mining and power industries. In Japan, gear and crowned tooth couplings mostly follow standards such as JIS B 1452, with representative manufacturers including Sumitomo Heavy Industries and NTN. Their products emphasize modular design and high consistency, and are mature in precision transmission. Compared with domestic GICL series, Japanese products have richer experience in tooth crowning, noise control and batch stability, but purchase price and lead time are usually higher. Standard systems differ markedly: domestic products follow GB/T crowned tooth coupling standards, Japan uses JIS, the US uses AGMA, and Europe uses DIN/ISO. During selection, note the differences in torque and speed units (N·m vs lb·in) and allowable misalignment definitions; do not apply parameters directly across systems. Whether domestic or imported, correct installation, alignment and lubrication are prerequisites for coupling life. Mastering standard differences and structural features lets the crowned tooth coupling perform reliably in the transmission system.