As the world's biggest energy consumer and CO_2 emitter,China commits,on the Paris Climate Change Negotiation,to reduce carbon intensity of GDP by around 60% to 65% between 2005 and 2030. In addition,Chinese government's Thirteenth Five Year Plan (13th FYP) aims to reduce emissions intensity of GDP by 40% to 45% cent between 2005 and 2020. Given these targets, and by using the most recent input-output table,the current study constructs a sector structure optimization (SSO) model. Authors derive the optimal sectoral structure subject to the constraints of total energy use and total CO_2 emissions. Authors also estimate the maximum emissions potential at the current technological level. Results from linear programming show that: ① the optimal sectoral structure satisfies the upper limit of China's GDP growth target with an annual average growth rate of 8%. Under the optimal structure, between 2005 and 2020,emissions intensity and energy intensity falls by 46.93% and 26.04% respectively,both reaching the 13th FYP targets. China's total emissions could fall further by about 14% under the premise that China's GDP grows at the lower limit rate of 6.5% per annum. ② The construction and transportation and storage sectors will remain vital and their shares in GDP should still increase. ③ Regarding the production structure,it must shift towards the services sector. The share of the services sector should increase,especially that of the residential services. ④ Under the'green and low-carbon'constraints,more than half of the industry sectors'production scales should fall,especially the energy and mineral processing industries.