In order to improve the heat pump drying (HPD) efficiency and improve the quality characteristics of dried scallop adductors, different kinds of osmotic agent (inulin, trehalose, maltodextrin and whey protein isolate) and mass concentrations (50g/L, 100g/L and 150g/L) were used to treated scallop adductors, and subsequently HPD was performed at temperature of 45℃ and air velocity of 2m/s. The effects of pretreatment with different osmotic agents on the drying kinetics and quality characteristics of scallop adductors were evaluated. The water state and distribution during HPD of scallop adductors were also analyzed based on low field nuclear magnetic resonance (LF-NMR) technology. The results showed that suitable osmotic agent pretreatment of inulin, trehalose, maltodextrin, and whey protein isolate could significantly improve the HPD rate, reduce the total color difference (ΔE) and improve the rehydration efficiency. Taking the comprehensive weighted score as the evaluation index, the optimal mass concentrations of inulin, trehalose, maltodextrin, and whey protein isolate were 100g/L, 150g/L, 100g/L and 50g/L, which were increased by 2.98%, 12.76%, 11.91% and 7.13%, respectively, compared with the control group. The trehalose treatment with a mass concentration of 150g/L had the best advantage in improving the drying rate and quality characteristics of dried scallop adductors. Compared with the control group, the drying time was shortened by 2h, ΔE decreased by 40%, the hardness decreased and the rehydration rate increased by 22.79%. The comprehensive weighted score increased by 12.76% compared with the control group. The LF-NMR results showed that the decrease of water content in scallop adductors during HPD mainly depended on the removal of immobilized water. After pretreatment with suitable concentration of osmotic agent, the migration rate of immobilized water in scallop column increased, the proportion of the free water peak area increased slightly, but the overall change was not significant. The proportion of the bound water peak area increased, whereas, the immobilized water peak area decreased. In addition, the transverse relaxation time shifted to the left during drying, signifying the decreased fluidity of water molecules. The optimum osmotic agent pretreatment for scallop adductors during HPD was 150g/L trehalose.