As a kind of clean energy, the demand for natural gas is increasing. However, China's natural gas resources are limited, and their demand growth rate is much higher than the supply. The coal-to-natural gas project alleviates the shortage of natural gas in China by using the abundant coal resources, but it has the problems of single product and poor ability to deal with risks. The coal-to-synthetic natural gas (SNG)/methanol polygeneration process can solve this by coproducing chemicals and have the advantages of high economic benefit and energy saving. The impact of polygeneration process design on carbon emission reduction is still the key issue to be solved urgently. Regarding the coal-to-synthetic natural gas (SNG)/methanol polygeneration process, this paper explores the interaction between polygeneration process design and carbon emissions by using life-cycle assessment method. From the perspective of life cycle, the amount of climate change is evaluated systematically, and the emission factors of each stage are listed. Through sensitivity analysis and Monte Carlo analysis, the breakthrough points of energy saving and carbon emission reduction are found, and the effective carbon emission reduction strategy is also proposed.