In this work, computational fluid dynamics software was used to numerically simulate the turbulent flow and heat transfer performance of the shell side fluid of the spiral casing heat exchanger with a threaded tube. The effect of Reynolds number and groove height on the turbulent flow and heat transfer performance of the shell side fluid was investigated. The field synergy principle was used to reveal the mechanism of fluid heat transfer enhancement by thread compound spiral flow. The results showed that the thread protrusions of the threaded inner tube had a significant effect on the disturbance and conduction of shell side fluid of the spiral casing heat exchanger, and the heat transfer efficiency of the shell side fluid of the spiral casing heat exchanger with the inner tube as a threaded tube was up to 22.1% higher than that of the model with the inner tube as a smooth tube. When the structural parameters were the same, with the increase of Reynolds number, Nusselt number of the shell side fluid of the spiral casing heat exchanger gradually increased, flow resistance gradually decreased, and the comprehensive evaluation factor ψ gradually decreased. Within the scope of the research, Nusselt number increased by 85.6, flow resistance decreased by 0.008, and the comprehensive evaluation factor ψ decreased from 1.35 to 1.18. When Reynolds number was certain, the equivalent height h' increased, flow resistance gradually increased, and Nusselt number first increased and then decreased. According to the analysis of field synergy principle, when the equivalent height h' was 0.220, the temperature field and velocity field synergy performance of the shell side fluid was better under the action of thread protrusion disturbance and diversion, and the comprehensive evaluation factor ψ was the largest. The optimal equivalent height h' of the thread should be about 0.220.