In order to meet the current environmental protection ultra-low pollutant emission requirements, one-step combustion is changed into two-step combustion by split-phase gasification combustion technology, and double-furnace structure, graded air distribution, calcium injection desulfurization, and combined denitrification with selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) are adopted to reduce pollutant emissions. ansys was used to establish a two-dimensional steady-state structure model of pulverized coal boiler with a double-furnace. Finite element analysis was carried out on the combustion in 54 MW, 56 MW, and 58 MW working conditions under different calcium-sulfur (Ca/S) ratios. The results showed that the desulfurization efficiency increased gradually when the Ca/S ratio was between 1.0 and 2.6 under the three working conditions. The desulfurization efficiency has no noticeable change when it is between 2.6 and 2.8, and begins to decline when it is greater than 2.8. The optimal calcium-sulfur ratio is obtained when the calcium-sulfur ratio is 2.6, and the SO2 concentration at the outlet of the furnace is reduced to 0.0001 mg/m3. By controlling the highest temperature in the furnace and adjusting the amount of denitrification agent, the nitrogen oxide emission at the outlet of the furnace is reduced to 0.87 mg/m3.