A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al(iBu)3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calculated based on the Kelen-Tüds(K-T) method and the Mao-Huglin(M-H) method. The influence of temperature on copolymer composition and polymerization rate was discussed in detail. The increase of reaction temperature brought the decrease of butadiene reactivity ratio rBd and supplied an effective adjustment on copolymers’ composition distribution. A series of trans-1,4-butadiene / isoprene copolymers were prepared using the catalyst system TiCl4 / MgCl2-Al (iBu) 3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calculated based on the Kelen-Tüds KT) method and the Mao-Huglin (MH) method. The influence of temperature on copolymer composition and polymerization rate was discussed in detail. The increase of reaction temperature brought the decrease of butadiene reactivity ratio rBd and supplied an effective adjustment on copolymers’ composition distribution.