Two-dimensional tungsten disulfide (WS ₂), as a semiconductor material with unique layer-dependent electronic and optoelectronic characteristics, demonstrates a promising application prospect in the field of optoelectronic devices. The fabrication of wafer-scale monolayer WS ₂films is currently a critical challenge that propels their application in advanced transistors and integrated circuits. Chemical vapor deposition (CVD) is a feasible technique for fabricating large-area, high-quality monolayer WS ₂films, yet the complexity of its growth process results in low growth efficiency and inconsistent film quality of WS ₂. In order to guide experimental efforts to diminish grain boundaries in WS ₂, thereby improving film quality to enhance electronic performance and mechanical stability, this study investigates the nucleation mechanisms of WS ₂during CVD growth through first-principles theoretical calculations. By considering chemical potential as a crucial variable, we analyze the growth energy curves of WS ₂under diverse experimental conditions. Our findings demonstrate that modulating the temperature or pressure of the tungsten and sulfur precursors can decisively influence the nucleation rate of WS ₂. Notably, the nucleation rate reaches a peak at a tungsten source temperature of 1250 K, while an increase in sulfur source temperature or a decrease in pressure can suppress the nucleation rate, thereby enhancing the crystallinity and uniformity of monolayer WS ₂. These insights not only furnish a robust theoretical foundation for experimentally fine-tuning the nucleation rate as needed but also provide strategic guidance for optimizing experimental parameters to refine the crystallinity and uniformity of monolayer WS ₂films. Such advancements are expected to accelerate the deployment of WS ₂materials in a range of high-performance electronic devices, marking a significant stride in the field of materials science and industrial applications.