This paper discusses the two major root causes of smog in China. The first one is the distributed coal combustion in many small and medium sized boilers which have no emission control systems installed. To resolve this problem, there are several ways, such as increasing the centralized coal combustion for heat and power cogeneration; or converting coal to SNG in areas where there is enough water resource and removing the pollutants of the coal in the centralized coal to SNG plant, or refining the coal and making it cleaner first before combustion. The second major cause of smog is the low quality diesel and outdated diesel engines used in China. To solve this problem, there are some ways, such as improving the diesel quality to meet the national V standard, and meanwhile, enhancing the law enforcement to eliminate these outdated diesel engines that do not meet the national emission standards; in addition, combusting cleaner and cheaper fuel such as methanol or DME in the diesel engines is also an option for certain areas where there are abundant alternative fuels such as methanol to replace diesel.