Abstract: High-grade pyrolusite was decreased via biomass vacuum pyrolysis with corn straw as a reductant. The effects of reduction temperature, reduction time, mass ratio of pyrolusite to corn stalks, and system residual pressure on the MnO yield were investigated. The results showed that when the reduction temperature was 873.15 K, the reduction time was 90min, the mass ratio of pyrolusite to corn straw was 16.67%, and the residual pressure was 500 Pa, the yield of MnO could reach 92.5%. XRD results of the reducing slag indicate that the reduction process of pyrolusite with corn straw as the reductant successively experiences phase transformation of MnO₂→Mn₂O₃→Mn₃O₄→MnO. Within the temperature range of 723.15~973.15 K, the vacuum pyrolysis biomass reduction process of soft manganese ore is controlled by interface chemical reactions, with an apparent activation energy of 30.7929 kJ/mol. The kinetic equation of the reduction process is given by: 1−(1−η)^(1/3)=1.7e^(3703.61/T)t.