Objective: To improve the quality of dried pitaya products. Methods: Based on the porous medium theory and Fick's law, a mathematical model of the coupling of heat and mass transfer of pitaya fruit with multiple physical fields of solid mechanics was established, and the variation of temperature and moisture content of pitaya fruit during the heat pump drying process was studied. Results: The calculation accuracy of the model considering volume shrinkage was higher. The maximum relative error between the calculated value and the test value was 9.2% after reaching the drying standard. The temperature distribution of pitaya slices decreased gradually from the surface to the center in the early stage of drying, and achieved a balance later, while the water distribution showed an opposite trend. The temperature and humidity gradient forces in the heat pump drying process were the main factors leading to the shrinkage deformation of pitaya slices. The calculated values of dry base moisture content of pitaya slices under different drying temperature and slice thickness were consistent with the experimental values, and the relative errors were all less than 10%, which proved the accuracy of the model. Conclusion: The mathematical model established by the experiment can accurately simulate the heat pump drying process of Pitaya.