【Objective】High soil penetration resistance (PR) limits the global crop growth and sustainable agricultural productivity. Heavy soil texture, poor soil organic matter, and low topsoil water content during summer have significantly increased the occurrence of high PR under a subtropical monsoon climate in southern China. The objectives were to investigate the penetration resistance characteristic model of red soils with different parent materials and influencing factors and explore the ameliorative effects of mechanical- and bio-tillage on PR in clayey Ultisols. 【Methods】This study investigated four red soils derived from different parent materials in China’s humid subtropical climate, including granitic (GS), Quaternary red clayey (CS), argillaceous shale (AS), and red sandstone red soil (SS). Key parameters measured included soil PR, water content (SWC), bulk density (?), organic matter (SOM) and texture. We analyzed the applicability of various PR models and their influencing factors, explored the ameliorative effects of mechanical- and bio-tillage on PR in clayey Ultisols, and identified the red soil PR thresholds of different parent materials by the least limiting water range. 【Results】Among the five characteristic models of soil PR, the saturated stress model provided a better fit (lower SSE and higher R2) for the four red soils, followed by water content model, water content and bulk density model, and soil matric potential model. The PR in red soils increased with decreasing water content, exhibiting a sharp increase once the water content fell below a critical value (~ 0.38 cm3· cm-3). The PR of low bulk density soils (1.3 g· cm-3) experienced a sharp increase at low water contents, whereas that of high bulk density soils (1.5 g·cm-3) showed a dramatic increase at high water contents. Soil texture (clay) was a primary factor influencing PR of different parent material red soils, while organic matter had negligible effects. Mechanical tillage reduced PR by ~963 kPa in the 0~40 cm depth compared to CK, whereas bio-tillage achieved reduction of ~785 kPa in the same depth and reduced PR (~1500 kPa) in the subsoil. The PR thresholds of the four red soils exceeded 2500 kPa, and thresholds for clayey red soils higher than those for sandy red soils. 【Conclusion】The saturated stress model water content model were applicable to four red soils in southern China. SWC, ? and texture played the primary factors influencing PR across different parent material red soils, with clayey red soils (CS and AS) exhibiting higher PR thresholds than sandy red soils (GS and SS). This research provides a scientific basis for identifying the occurrence of seasonal drought and rationally selecting tillage practices for drought prevention in subtropical red soil regions of China through the lens of soil penetration resistance.