An experimental study on the performance of freeze-dryer's cold trap has been carried out under different temperature of the cold trap coil and different frost thickness in the paper. Research results reveal that the capture efficiency of cold trap increases with the decrease of the temperature of cold trap coil

and the overall heat transfer coefficient of the cold trap decreases with the increase of frost accumulation on the surface of the cold trap coil. A theoretical analysis on the convection heat transfer in the cold trap shows that the convection heat transfer decreases with the increase of the degree of vacuum

and the convective heat transfer needn't to be considered when the fluid in the cold trap is in the state of free-molecule flow.