Abstract: Polyisoprene-b-poly(methyl methacrylate)(PI-b-PMMA) was synthesized by anionic polymerization using n-BuLi as the initiator in tetrahydrofuran cyclohexane mixed solvent. P complex with large steric hindrance and special electric charge environment was used as an additive in the system. The molecular structure of prepared block copolymers was characterized by GPC and 1H-NMR. Results showed that the conversion decreased with the increasing of the volume ratio of tetrahydrofuran cyclohexane. P complex could inhibit the side reactions of MMA effectively, which can partially block the channels between positive and negative ions. Due to the introduction of P complex, PI-b-PMMA with narrow molecular weight distribution(1.21) was synthesized successfully at 0 ℃ and easy to be industrialized. The PI chains in the copolymer were mainly composed of 3,4 structure.