The block copolymer of PSt-b-POEOMA-b-PSt with the end of -COOH functional group has been synthesized by reversible addition fragmentation chain-transfer (RAFT) using S,S′-Bis(α,α′-dimethyl-α-acetic acid)-trithiocarbonate (BDATC) as the chain transfer agent. The block copolymer containing hydrophilic end groups can be assembled into the core-shell nanoparticles for drug-loaded polymer template. The architecture of the copolymer was confirmed by FTIR, 1H NMR spectra and GPC. Furthermore, through the thermogravimetric (TG) and differential scanning calorimetry calorimeter (DSC) methods, the thermal properties of the three different proportions of block copolymers were studied. Results showed that RAFT polymerization was successful to synthesize the designed block copolymer; the molecular weight distribution of the controlled block copolymer was about 1.35. And the block copolymers had good thermal stability; the compatibility of the two components could be speculated by the change of the glass transition temperature (Tg).