Abstract: In order to ensure the security of underground biogas digester structure, the static, active and passive earth pressure of three kinds of soil were compared based on Rankine earth pressure theory, and earth pressure value on pool wall of underground biogas digester was determined. According to linear elastic finite-element analysis, the mechanical behavior of three different pool covers, such as slab, shell and truncated cone, were analyzed. The results showed that the earth pressure on pool wall could be considered as static earth pressure, and ring beam can make the maximum stress of truncated cone pool cover with circular opening decrease by 40%. It is necessary to set ring beam with it.