To research and develop sustained-release tablets of metformin hydrochloride with a o dual controlled release-system and to investigate the optimization of tablet core and coating formulations and their releasing mechanism.Using hydrogenated castor oil as a controlled release waxy material for the core and Eudragit NE30D as a controlled release material for the semipermeable coating, the target tablets were preparedBased on the investigation into appearance, hardness, fluidity, tablet ability and release rate of the tablets, the core and coating formulations were screened for optimization.In vitro release rate of the tablets was not affected by release medium and revolution.The core prepared with formulation 9 was smooth, with good hardness, fluidity, tablet ability and release rate (40.2%, 56.8%, and 85.7% resp. at 0.5, 1, and 3 h).The tablets coated with formulation 5 showed release rates of 50% and 80%, resp. at 5 and 8 h.The target tablets could release steadily for 12 h and their release behavior agreed with first-order equation.These results show that the tech. process for the target tablets, which showed a steady and sustained release, is easy to operate.