Abstract: The process of sinking open caisson was analyzed.The earth pressure on the foot blade of a open caisson was the passive earth pressure,while the earth pressure on the wall of a open caisson was the active earth pressure or the earth pressure at rest.Based on the theory of failure of subsoil,the compressed core sinking with the open caisson was regarded as part of the foundation,then the displacement of soil,the height and the width of the foot blade of a open caisson and the changes of the properties of soil were analyzed in the process of sinking of open caisson.The value of passive earth pressure on the foot blade of open caisson varied between the value of the earth pressure at rest and the limit value of passive earth pressure.Based on the coefficient of passive earth pressure,the formulas of passive earth pressure on open caisson and lateral friction of sinking open caisson were given.Using these formulas,the structure of a underground whirling pool in a factory was analyzed and compared.It is pointed out that the height and the width of the foot blade of open caisson have great influence upon the lateral friction and the coefficient of sinking.