Abstract: For the domestic development of cesium atom clock with high performance and small volume，it is essential to study on the oversea technology of preventing liquid cesium to spill from the orifice of an oven inside a small cesium beam tube（CBT）.In this paper，based on the overseas cesium-ovens of ground and spaceborne CBTs，the authors clarified clearly the physical mechanism on how porous material could avoid liquid cesium to spill in a CBT by considering the especial roles of porous material and liquid in damper and separator，respectively.Furthermore，physical parameters of porous material were analyzed simply with a method of fluid dynamics.The key items of process design for spill-resistant oven were emphasized.All results are beneficial for yield of cesium beam with high quality.