The self-assembly behavior of (AB)(f) star copolymers under a cylindrical confinement has been investigated using self-consistent field theory. Aiming to study the influence of the pore diameter on the order-order transitions as volume fraction varies, the phase diagram with respect to the volume fraction and the pore size is constructed. An interesting transition sequence of ordered nanostructures, H-2(A)-> P-2(A)-> L-2(A)-> P3CB -> H3CB, is predicted, which is corresponding to the phase transition of C -> G -> L -> G -> C in bulk. Notably, this transition sequence is universal for both linear (AB diblock and BAB triblock) and star-like (AB) f block copolymer. In particular, we explore the formation mechanism of helical nanostructures as the volume fraction increases, where the P phase plays an important role in forming helical structures as an intermediate nanostructure. Finally, we construct the twodimensional phase diagram, including pore size and volume fraction, of (AB)(f) star-like block under confinement at different number of arms, where P nanostructures was found to surrounded by other nanophases suggesting the importance of P nanostructure in the transition sequence.