Abstract: The effects of energy density,power polarity and electrode interval on removal efficiency of microorganisms and particulates in indoor air were investigated using a needle-to-hole DC corona discharge plasma reactor. The removal mechanisms were analyzed. The results show that the DC corona discharge plasma reactor has good performance in removing microorganisms with different sizes(0.65~2.1 μm, > 2.1 μm) and coarse particulates(TSP and PM₁₀),however,incapable of removing fine particulates(PM_2.5). Compared with positive DC corona discharge,negative DC corona discharge behaves better in removing paticulates,however,worse in removing microorganisms. Under the same conditions,the removal efficiency of fungi is higher than that of bacteria. These observations can be explained by the difference in the composition of plasma generated by positive and negative DC corona discharge as well as different resistance abilities of different microorganisms to plasma oxidation. As microorganisms can be inactivated by plasma species besides being removed by electrostatic precipitation in the electric field,its removal efficiengy is higher than that of particulates under the same conditions.