This paper describes a study on the performance of steam ejector by variation of steam pressure. Water temperature is especially important for good quality of fish in an inland aquafam. In summer season, the water temperature increases above 25℃, but for good quality breeding or fish is the maintenance of optimum aquafam temperature by about 20℃. Therefore it is needed to drop the water temperature to provide suitable conditions of fish growth. There are many kinds of cooling system, in this study using steam ejector. After cooling the water in vacuum tank with the steam ejector then circulate this water to inland aquafam. In this way to minimizes fish stress that it is caused by water temperature. The objective of research confirms the difference of the case which there is no water in the vacuum tank and has water in the vacuum tank. The purpose of this paper is to examine the effects on the performance of steam ejector by variation of steam pressure.