The stimuli-responsive membrane with ON/OFF-switchable pores has various applications such as targeted drug delivery and biosensor. In this work, the perforated vesicle/membrane self-assembled from ABA triblock copolymers is explored by dissipative particle dynamics. The inflexibility in hydrophobic B-blocks (kθ) is the key factor for membrane perforation. Flexible copolymers (kθ = 0) tend to yield an intact membrane with I- and U-shaped polymer conformations; however, as the inflexibility increases, the U-conformation diminishes and pores begin to emerge. Membrane perforation can be clearly identified by the leaking process of the solvents from the interior of the vesicle. On the basis of energy analyses, spontaneous perforation is mainly driven by the orientation entropy of semi-rigid B-blocks. The ON/OFF of the pores can be further regulated by the environmental stimuli, which cause changes in the compatibility between A- and B-blocks and the hydrophobicity of hydrophilic A-blocks. As A- and B-blocks become more compatible, the orientation entropy of B-blocks can be regained without the existence of pores, leading to the disappearance of perforation. On the other hand, as the hydrophobicity increases, A-blocks reduce their contacts with water, resulting in pore shrinkage (switch-OFF state) as well. Our results shed light on screening suitable copolymers for perforated smart membranes.