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In order to investigate the enhancing effect of contact ultrasound treatment on conventional heat pump drying, an ultrasound device was installed in the heat pump dryer, and contact ultrasound reinforced heat pump drying of apple slices was carried out to study the effects of ultrasound power, drying temperature and sample thickness on drying characteristics. The results showed that the internal mass transfer process of samples could be enhanced by putting samples on the ultrasound radiation board directly during heat pump drying. Drying time was shortened and drying rate was improved with the increases of ultrasound power and drying temperature and the decrease of sample thickness. The influence of ultrasound treatment on drying rate was decreased with the reduction of moisture content. Obviously strengthened effect of contact ultrasound on drying rate could be observed at low temperature and thin thickness, while it was reduced with the increases of drying temperature and thickness. The values of effective moisture diffusivity ( D eff ) ranged from 1.333×10 -10 m 2 /s to 1.651×10 -9 m 2 /s, and it was increased at high ultrasound power and drying temperature. After the contact ultrasound treatment, the numbers and sizes of the tiny holes inside apple slice were improved. With ultrasound power of 60 W, many micro-tunnels were even produced in the organizational structure of apple slices, which was also beneficial to enhance internal moisture diffusion. Therefore, contact ultrasound technology is an effective method to increase the drying rate of heat pump drying and shorten drying time obviously as well.