The pullout resistance is a design consideration for suction caisson-supported offshore structures, such as offshore platforms and wind turbines. An analytical method is proposed in this paper to calculate the pullout resistance of a single caisson foundation embedded in clay. Comparisons with laboratory model tests were also made to verify the accuracy of the proposed analytical method. Parametric studies were conducted to investigate the effects of key factors on the pullout resistance of caisson. This study found the pullout force nonlinearly increases with the increase of caisson diameter squared but linearly increases with the increase of caisson–soil frictions. For caisson wall thickness over height ratio ranging from 0.00125 to 0.00325 and caisson diameter over height ratio ranging from 0.25 to 0.75, the normal stress decreases nonlinearly along with the depth of the caisson skirt wall and is heavily influenced by the skirt wall thickness but slightly influenced by caisson diameter.