Abstract: A method for preparing hydrogen from ammonia by using pressure swing adsorption (PSA) is provided. The method for preparing hydrogen from ammonia, of the present invention, comprises the steps of: generating hydrogen and nitrogen from ammonia gas through a high-temperature reaction by using a catalyst; performing purification by selectively adsorbing unreacted ammonia gas from a gas containing unreacted ammonia and low-purity hydrogen and nitrogen, which are supplied through the high-temperature reaction and cooled; and performing purification by separating high-purity hydrogen from the gas consisting of low-purity hydrogen and nitrogen, wherein purification is carried out by using a carbon molecular sieve (CMS) adsorbent so as to desorb the unreacted ammonia gas through PSA.