In the process of underground coal gasification (UCG), there have been doubts or controversies if it is possible to control pollution of heavy metals such as arsenic and cadmium. To eliminate this suspicion, this paper first investigated the control method and design flow of reducing heavy metal pollution in the process of underground coal gasification (UCG) without shaft based on the analysis of the potential arsenic and cadmium pollution forms. The relationships between the development height of underground gasification mining-induced fractures and the parameters of gasifiers was revealed. The findings indicated that: 1) By rationally designing the parameters of the gasifier, it can be possible to control the development of mining-induced fractures, thus ensuring that the underground combustion space area does not penetrate the aquifer, surface water and atmospheric environment. Consequently, the pollution of arsenic and cadmium caused by UCG without shaft can be controlled from the source. Meanwhile, the validity of this method was verified from an engineering example. 2)When the gasifier height was constant and the isolated coal pillar was stable, the gasifier width was linearly positively correlated with the development height of the mining-induced fracture; When the widths of the gasifier and the isolated coal pillar were constant, the gasifier height and the development height of the mining-induced fracture was also linearly positively associated. As the contents of arsenic and cadmium in coal are high in China and the United States, the arsenic and cadmium control methods during the underground coal gasification proposed in this paper have valuable application prospects in these two major coal countries.