A series of novel pseudo-cryptand-containing copolymers (PDStPEG(m)MA) with different sizes were constructed by maleic anhydride (MAn)-assisted reversible addition fragmentation chain transfer (RAFT) alternative cyclopolymerization of distyrenic 18 -membered macrocycle derivatives. Pyrene and hydrophilic methoxypoly(ethylene glycol)s (MPEG) segments were then grafted onto the polymer backbone by amidation and esterification reactions and thus endowed polymers with fluorescent properties and water solubility, respectively. The size-dependent ion recognition property of these pseudo-cryptand-containing copolymers against metal ions was also investigated by fluorescent spectra. With the water solubility and biocompatibility, PDStPEG(2)MA(10-g-py-g-)MPEG can be effectively employed as fluorescent sensors, especially for Al3+ detection in vitro.