Objective: The paper analyzes the non-linear relationship and reasons of rural medical assistance fund in alleviating poverty caused by illness in China central and western regions. Methods: Based on the PSTR model, the paper applies the data of China central and western Regions from 2010 to 2018. Results: The rural medical assistance fund in China central and western regions has a significant nonlinear relationship and a double threshold asymmetry characteristic to the rural poverty caused by illness. When the per capita disposable income of provincial rural residents accounted for 195.70% of the per capita disposable income of China rural residents, a nonlinear transformation occurred. In China central and western low-income regions, the impact of medical assistance funds on rural poverty caused by illness is not significant, however, in high-income regions, the anti-poverty effect is significant. Conclusion: The relatively low medical assistance fund in China central and western low-income regions can not form a strong anti-poverty effect. It is suggested that different medical assistance policies should be implemented in China central and western low-income regions and high-income regions to improve the anti-poverty efficiency of medical assistance funds.