Soil acidification has become one of the key factors limiting agricultural productivity and ecosystem stability. Biochar, as a potential remediation material, has been widely applied to mitigate soil acidification. Based on 110 peer-reviewed articles from the CNKI (China National Knowledge Infrastructure) and Web of Science databases, this study evaluated the effect of biochar application on acidified red soils using meta-analysis and employed the ARIMA model to predict future changes in soil pH, and proposed four core mechanisms by which biochar improves red soil acidity: direct neutralization effect; indirect buffering effect; cumulative effect over time; and structural optimization effect. Additionally, four hypotheses were established: 1) biochar type significantly modulates the strength of the direct neutralization effect; 2) application rate of biochar significantly influences the stability of the indirect buffering effect; 3) application duration of biochar significantly impacts the cumulative effect; 4) soil depth significantly affects the structural optimization effect. The results showed that biochar application can significantly increase soil pH (average increase of 16.2%), reduce exchangeable acidity (average decrease of 48.3%), and enhance cation exchange capacity (average increase of 31.0%). Further analysis revealed significant differences in improvement effects based on biochar type, application rate, and soil depth, with a nonlinear saturation trend observed in soil pH response to application rate of biochar. Using the ARIMA time series model, the red soil pH is predicted to stabilize at 5.2.