Single biochar application has remarkable potential to improve soil ecosystem multifunctionality (SEMF) and crop yield because of its legacy effect or residual effect. However, the legacy effect (i.e., duration and magnitude) of single biochar application, especially for acidic soil is far from thoroughly understood. A field experiment with the single factor randomized block design in an acidic paddy in South China was conducted from 2015 to 2019 to explore the legacy effects of single biochar application (0, 20, 40, 60, 80, and 100 t ha-1) on SEMF and its contribution to rice yield. The results showed that: (1) The duration of the legacy effect (i.e., the time the SEMF showed significant differences with that of zero biochar application) lasted three years consistently for different biochar application rates ranging from 20 to 100 t ha-1. (2) The magnitudes of the legacy effect (i.e., the relative change of SEMF compared with that of zero biochar application) were higher with more biochar application, but their differences decreased temporally. (3) SEMF and rice yield showed significant positive relationships for all five years. Biochar application increased SEMF, which further increased rice yield directly and indirectly through increasing the aboveground biomass of rice at the fulling stage, the number of grains per panicle, and the seed setting rate. This study extended our understanding of the legacy effect of single biochar application on SEMF and its contribution to rice yield in an acidic paddy and uncovered the paths of increasing rice yield through improving SEMF. These findings have valuable implications for single biochar application in acidic paddy, for example, adding biochar every three years.