A mathematical model based on the Lucas-Washburn equation has been developed to address the relations of the capillary height, capillary radius and the heat flux in a capillary column and the equation is extended to a capillary loop for investigating the stability of the condensing interface with phase change by some simplifications in the paper. The stability of the condensing interface is studied by introducing a small disturbance into capillary height. The dynamics performances of the condensing interface under three different operating conditions are discussed in this paper. The results show that the condensing interface presents high instability under non-gravitational condition, while the stability can be enhanced in gravitational condition with a certain gravitational height, moreover, regular vibration can be formed on the condensing interface due to the periodic oscillation of the pressure in the system. (C) 2011 Elsevier Ltd. All rights reserved.