A processor and a method for executing load operation and store operation thereof are provided. The processor includes a data cache and a store buffer. When executing a store operation, if the address of the store operation is the same as the address of an existing entry in the store buffer, the data of the store operation is merged into the existing entry. When executing a load operation, if there is a memory dependency between an existing entry in the store buffer and the load operation, and the existing entry includes the complete data required by the load operation, the complete data is provided by the existing entry alone. If the existing entry does not include the complete data, the complete data is generated by assembling the existing entry and a corresponding entry in the data cache.