A novel water-soluble pH stimuli-responsive fluorescent copolymer of P(PEGMA-b-(MAH-co-Rh6GEAm)) was synthesized by two-step sequential RAFT polymerization. The prodrug with drug content of 0.1560 mg/mg was prepared by coupling doxorubicin (DOX) onto the copolymer via acid-cleavable hydrazone bond, formed between the carbonyl group of DOX and abundant hydrazide functional groups in the copolymer. The amphiphilic DOX-conjugated prodrug (P(PEGMA-b-(MAH-DOX-co-Rh6GEAm))) could easily form a micelle in water with Dh of less than 100 nm. It could be transported into HepG2 cells and release DOX without burst release, while the leakage of DOX can be avoided in the simulated normal physiological media. Furthermore, its fluorescence intensity experienced a reversible change with the transformation of the media pH. The better biocompatibility, pH stimuli-responsiveness, and the strong fluorescence at low pH media make the nanoparticles a potential platform for the controlled release of anticarcinogens and real-time fluorescent imaging of tumor tissues.