The performance of closed heat pump dryer was investigated.The indexes of coefficient of performance of heat pump systems COP,specific dehydration power consumption SPC,average specific dehumidification MER,specific dehumidification SMER and so on were used to study its performance.The results indicate that the value of COP increases with the increase of moisture content at the lower load,and it arrives at the highest value when the moisture content is 45% at the higher load.The SMER of heat pump and drying system increases with the increase of moisture content at the lower load,and it basically remains at a high value when the load is higher.Because the heat pump system and drying system restrict and interact with each other,the values of COP and SMER can’t reach its highest value simultanuously.