Hydrogen Generator by Ammonia Decomposition with Purifying System is very low cost; it has long service life, simple operation, compact structure, small coverage, and is very simple to install. Liquid ammonia is used as source for hydrogen generator. The liquid ammonia is vaporized and is heated by decomposition with catalyst into mixed gas containing 75% hydrogen and 25% nitrogen. Based on the principle that the molecular sieve adsorbs different ammonia and water at different temperatures, high purity gas will be produced by heat regenerating through working at normal temperature.