Abstract: An in-phase system with computer and displacement sensors for temperature collection were developed to investigate experimentally the influence of temperature and time during the second step foaming procedure on the characteristics of cell-structure (diameter and uniformity) of Al alloy foam.The effect of preheating technology on cell-structure of Al alloy foam was also discussed.The results show that the process of two-step foaming could be divided into three phases of initiation,raising and collapse stage.Non-uniform temperature field during two-step foaming caused the difficulty of achieving uniform cell-structure of Al alloy foam.Al alloy foam with satisfactory cell-structure could be fabricated through promoting the temperature condition by preheating procedure.