It was studied the performance characteristics such as specific moisture extraction rate (SMER) of closed heat pump drying system with the condition of different air mass-flow-rate, relative humidity and with or without heat pipe. The results showed that the effects of heat pipe on SMER of closed heat pump drying system were very significant, and the application of heat pipe could enhance the system SMER by 20%~200% under test conditions. Under the condition of the constant temperature and constant relative humidity, the SMER of the system had a maximum value while the air mass-flow-rate was between 0.2~0.4 kg/s. With constant air mass-flow-rate and constant air temperature, the change of relative humidity had the most significant effect on SMER. While relative humidity increased from 25% to 75%, the SMER of closed system with heat pipe enhanced from 1.4~1.6 to 4.1~4.3, but the SMER without heat pipe from 1.1 to 3.0~3.1.