Abstract: Flow field of semi-dry flue gas desulphurization（FGD） reactor is depicted by means of computational fluid dynamics（CFD）.Through optimizing inner part of the reactor and increasing the reacting rate between SO₂ and desulphurization agents,SO₂ removal efficiency is improved.Based upon multi-phase flow pattern of the reactor,basic theories of k-ε equation and particle trajectory model are established,and the influence of inner structure of the reactor tower on the fluid flow and SO₂ removal efficiency analyzed.The results obtained here can indicate that reactor structure can help flue gas and flue gas distribution can control reaction and better removal efficiecy.