As an important means to cope with global warming, CO_2 emission reduction has became a hot topic at home and abroad. To study key technology of pre-combustion CO_2 capture system, based on Huaneng(TianJin) 265MW IGCC (integrated gasification combined cycle) demonstration power plant, approximately 10000m3/h syngas was extracted from the gasification unit for CO sulfur tolerant shift, MDEA desulphurization and decarbonization, PDS sulfur recovery technology research. Meanwhile, the process simulation, field testing and system analysis of China's first industrial scaled pre-combustion capture system was completed. The results showed that the full load capture capacity was 78.11 thousand ton per year and the capture unit energy consumption was 2.35 GJ/t(CO_2) with capture ratio≥85%. The simulation results fitted well with the actual operation data. The MDEA system accounted for 93.3% energy consumption of capture system and the thermal regeneration accounted for 81.61% of MDEA energy consumption. At the same time, the CO_2 loss process of the capture system was analyzed. With the application of the four-stage shift converter, the capture ratio increased to 92.29%, while the system consumption almost remained unchanged. The capture energy consumption and cost of CO_2 compression liquefaction was also investigated. The research results can provide theoretical guide for pre-combustion capture design, industrial enlargement and optimization.