In this investigation, a novel process for the synthesis of nano-ZrO₂ powders based on high-temperature mechanochemical technology (HTMT) in a short process is proposed and HTMT nano-ZrO₂ enhancement mechanism as an additive on the properties of B₄C ceramics was systematically investigated. ZrO(OH)₂ was used as a precursor, and ZrO₂-B₄C composites were prepared by optimizing the ball milling temperature and time in combination with the hot-press sintering technique. The results demonstrated that the high-temperature mechanical force causes the transition temperature of ZrO₂ from monoclinic to tetragonal crystal system to be decreased to 500 °C. The ZrO₂ treated by high-temperature ball milling at 600 °C/6 h exhibits lower microstress, higher crystallinity, and a particle size of only about 9.12 nm. HTMT nano-ZrO₂ effectively controls the size of in situ generated ZrB₂ particles in B₄C ceramics, reduces interfacial porosity and grain coarsening, and promotes densification of B₄C ceramics compared to commercially available nano-ZrO₂. With the addition of 4 wt% HTMT nano-ZrO₂, the composite showed optimal comprehensive properties: relative density of 99.75% (2.57 g/cm³), fracture toughness of 4.74 MPa/m^1/2, flexural strength of 266.61 MPa, Vickers hardness of 31.14 GPa, and fracture mode with mixed mechanism of through-crystallization and along-crystallization.