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 evaluates the effect of biochar application on acidified red soils using meta-analysis and employs the ARIMA model to predict future changes in soil pH. The study proposes four core mechanisms by which biochar improves red soil acidity: (1) direct neutralization effect; (2) indirect buffering effect; (3) cumulative effect over time; and (4) structural optimization effect. Additionally, four hypotheses were established: (H1) biochar type significantly modulates the strength of the direct neutralization effect; (H2) application rate significantly influences the stability of the indirect buffering effect; (H3) application duration significantly impacts the cumulative effect; (H4) soil depth significantly affects the structural optimization effect. The results show that biochar application significantly increases soil pH (average increase of 16.2%), reduces exchangeable acidity (average decrease of 48.3%), and enhances cation exchange capacity (average increase of 31.0%). Further analysis reveals 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.