Penetration of the suction caisson closely depends on the suction pressure. If the magnitude of suction is set to be smaller, it will lead to a lower penetration velocity and increasing construction costs. The soil plug rises higher otherwise. Thus, the suction caisson cannot reach the desired depth, resulting in either insufficient bearing capacity for the requirements of foundation design, or the failure of sand foundation due to piping. The aim of the paper is to determine a reasonable suction range to meet requirements of engineering practice. The minimum suction is determined by using the static equilibrium method. The critical value of suction is obtained by the formulation of the effective stresses on the inside and outside of the bucket wall in terms of the Hencky’s stress equation. The maximum suction is obtained by using the mechanism of sand piping inside bucket. In addition, the maximum penetration depth of the caisson is determined in terms of the maximum and minimum suctions. Finally, the proposed calculation of suction are verified by the published data, and they have a very good agreement.