With the development of the second generation pressurized fluidized-bed combustion combined cycle (PFBC-CC), integrated gasification combined cycle (IGCC) and the technology of staged combustion for lower emission of NOx, limestone desulphurization under a reducing atmosphere is gradually becoming a very important problem. This paper presents static tests of limestone desulphurization reaction under a reducing atmosphere. The experiment was done by an atmospheric thermogravimetric analyzer (TG-DTG8110, made in Japan). The sorbent is limestone from Nanjing, China. Its CaCO3 percentage is 93.75% and particle mean diameter is 0.63 mm. Mixed gas concentrations are as follows. (N-2 + H2S) mixed gas: [H2S] is 1.366E4, 2.277E4 and 2.73E4 mg (Nm(3))(-1); (O-2 + N-2) mixed gas: [O-2] is 3, 5, 7 and 100%. Test temperatures are 920-930 degrees C and 835-845 degrees C. The optimal reaction conditions were obtained from the experiment. Suiphidation reaction at about 925 degrees C and oxidation reaction at about 848 degrees C are carried out easily. Through numerical handling, the dynamic equations of sulphidation and oxidation reactions are also obtained.