【Objective】The loess area is arid with little rain and the soil is loose and porous. The water vapor in this area may play an important role in profiling water migration. Thus, it is important to study and understand the cyclic migration law of soil water vapor flux in unsaturated zone for realizing the sustainable development of water resources in arid regions. 【Method】To explore the flux transfer rule of liquid water and steam water in loess profile, based on the high-frequency in-situ monitoring test of dryland apple orchard profile (0-200 cm) in Loess area, the simulation of water-vapour-heat-air coupling STEMMUS (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil) model was adopted in this study. 【Result】Results show: (1) STEMMUS model reliably reproduced the dynamic changes of soil moisture (d was between 0.81 and 0.98, NRMSE was between 5.5% and 15%) and soil temperature (d was between 0.98 and 0.99, NRMSE was 1.4% and 4.6%) in the profile of dryland apple orchard. This showed good agreement with the simulation of apple tree evapotranspiration (d was between 0.92 and 0.96). (2) Rainfall had significant effects on matrix potential gradient, temperature gradient, liquid water and water vapor flux. The transport of liquid water and vapor water was mainly driven by the matrix potential gradient and temperature gradient, respectively. During the study period, the maximum recharge depths of the soil moisture was 100 cm and 160 cm, respectively, which indicates that soil water could migrate to deeper soil through downward vapor water. 【Conclusion】STEMMUS model considering soil spatial heterogeneity significantly improves the simulation accuracy and reveals the migration law of water vapor flux in loess profile. The research results can deepen the understanding of water migration in the loess profile.