Abstract: A transient model of a CPL has been developed to predict the thermal and dynamic behavior.This model comprises two coupled modules: the thermal module and the hydrodynamic module.The objective of this numerical model is to study the mechanisms of the unstable behavior during the cyclical functioning of the CPL.The simulative processes include the start-up,the temperature oscillations in the reservoir and the heat load change in the evaporator.The numerical results agree with the experimental data.Moreover,this model is used to explain the reason that the start-up becomes a failure easily,the abrupt change of the heat load can lead to the evaporator deprime.It also can reveal that the temperature oscillations in the reservoir are disadvantageous to the operation of CPL.