A series of phosphorus-containing copolyester prepolymers were first sythesized from dimethyl terephthalate (DMT), ethylene glycol (EG), and 2-carboxyethyl (phenyl)phosphinic acid (CEPPA) by molten transesterification and polycondensation, and then solid-state polymerization (SSP) was conducted for different reaction times (t(SSP)) so as to prepare higher molecular weight copolymers. The intrinsic viscosity was increased with the increase of t(ssp), but decreased with the increase of CEPPA content. The sequence distribution of resultant copolyesters was analyzed by H-1 NMR. It was found that the randomness of copolyesters was decreased after SSP, and the transesterification occurred mainly at the ester bonds formed by CEPPA and EG, resulting in the chain growth. DSC results showed that SSP treatment was favorable to enhance the crystallization ability of the obtained copolyesters.