The finite element method is used to investigate the ultimate lateral pressure of snowflake pile group in undrained clay in this paper. The parametric analyses are performed to study the effects of the geometry of cross-section, the pile-soil adhesion coefficient, the loading direction, and the normalized pile spacing on the ultimate lateral pressure and the damage mechanism of the snowflake pile. The analysis results show that the ultimate lateral pressure of snowflake pile group decreases with the increasing of the length-thickness ratio of the pile flange and increases with the increasing of the pile-soil adhesion coefficient. When the loading direction is considered, the snowflake pile group with the number of piles of 4 is less affected by the loading direction, it has a larger ultimate lateral pressure. The ultimate lateral pressure of the pile group significantly decreases with the increasing of the number of piles. When the pile spacing is smaller, the decreasing of the ultimate lateral pressure is more obvious with the increasing of the number of piles. On the basis of finite element analysis, the empirical formula of ultimate lateral pressure of snowflake pile group is proposed and calibrated with the finite element results.