Provided are a catalyst for hydrocarbon steam cracking for light olefin production and a method for preparing the same. The catalyst is a simple KMgPO4 catalyst, a supported KMgPO4 catalyst, or a KMgPO4-sintered catalyst. The supported KMgPO4 catalyst is prepared by impregnating a carrier with an aqueous solution of a KMgPO4 precursor and the KMgPO4-sintered catalyst is prepared by mixing a KMgPO4 powder or a KMgPO4 precursor powder with metal oxide followed by sintering. Provided is also a method for producing light olefins such as ethylene and propylene by steam cracking in the presence of the catalyst. When the catalyst comprising KMgSO4 as a catalytic component is used in olefin production, the yield of olefins is increased and the amount of cokes deposited on the catalyst is reduced.