This study investigates the intrinsic phase stability of ultrathin 2M WS₂, demonstrating that thinner samples exhibit significantly higher thermal stability compared to bulk counterparts. The 2M-to-2H phase transition temperature increases from 120°C to 210°C as the thickness of WS₂ decreases from bulk to bilayer. Monolayered 1T' WS₂ can withstand temperatures up to 350°C in air and 450°C in argon before transforming to the 1H phase. The enhanced stability of thinner 2M WS₂ is attributed to stiffened intralayer bonds, increased thermal conductivity, and higher average energy barriers per layer during phase transitions. Theoretical simulations confirm that thinner WS₂ has a higher average energy barrier per layer during the layer-by-layer phase transition process. The observed high intrinsic phase stability of ultrathin 2M WS₂ expands its practical applications in various fields, including superconductivity, electronics, and energy conversion. The study also reveals that the phase transition of WS₂ occurs layer-by-layer, with the transition barrier decreasing as the number of layers increases. The results highlight the importance of layer number in determining the electronic and phonon properties of 2D TMDs. The findings suggest that ultrathin 2M WS₂ has higher phase stability due to reduced interlayer interactions and enhanced intralayer bonding. The study provides insights into the phase transition mechanisms of WS₂ and offers a theoretical basis for understanding the stability of 2M TMDs under different conditions.This study investigates the intrinsic phase stability of ultrathin 2M WS₂, demonstrating that thinner samples exhibit significantly higher thermal stability compared to bulk counterparts. The 2M-to-2H phase transition temperature increases from 120°C to 210°C as the thickness of WS₂ decreases from bulk to bilayer. Monolayered 1T' WS₂ can withstand temperatures up to 350°C in air and 450°C in argon before transforming to the 1H phase. The enhanced stability of thinner 2M WS₂ is attributed to stiffened intralayer bonds, increased thermal conductivity, and higher average energy barriers per layer during phase transitions. Theoretical simulations confirm that thinner WS₂ has a higher average energy barrier per layer during the layer-by-layer phase transition process. The observed high intrinsic phase stability of ultrathin 2M WS₂ expands its practical applications in various fields, including superconductivity, electronics, and energy conversion. The study also reveals that the phase transition of WS₂ occurs layer-by-layer, with the transition barrier decreasing as the number of layers increases. The results highlight the importance of layer number in determining the electronic and phonon properties of 2D TMDs. The findings suggest that ultrathin 2M WS₂ has higher phase stability due to reduced interlayer interactions and enhanced intralayer bonding. The study provides insights into the phase transition mechanisms of WS₂ and offers a theoretical basis for understanding the stability of 2M TMDs under different conditions.