Abstract: This study presents a comprehensive investigation on the properties of negative capacitance field-effect transistors (NCFETs) based on the metal-ferroelectric-insulator-semiconductor (MFIS) structure with Hf_xZr_1−xO₂ (HZO, 0.5≤x≤0.9) thin film. The results indicate that the NCFETs exhibit excellent subthreshold swing (S_S) values, consistently below 60 mV·decade⁻¹, which is the theoretical physical limit of conventional Si-based field-effect transistors (FETs). The ferroelectric HZO composition significantly influences the longitudinal electric field, electron concentration, and hole concentration within the channel, thereby directly affecting the S_S and saturation current. Notably, the MFIS NCFET incorporating an Hf_0.5Zr_0.5O₂ ferroelectric layer exhibited the lowest S_S. Moreover, by modifying the dielectric material and channel length, variations in the trends of S_S and saturation current were observed. The device with ZrO₂ dielectric layer, characterized by the highest dielectric constant, demonstrated the lowest S_S of 47.49 mV·decade⁻¹. Furthermore, the S_S decreased as the channel length increased from 50 nm to 1000 nm. This research provides theoretical support for the performance optimization of low-power NCFETs and negative capacitance capacitors.