Abstract: Polyisoprene(PI) was synthesized by anionic polymerization using n BuLi as initiator, cyclohexane as solvent at 40-70 ℃. The effects of THF and P Complex on the polymerization and PI structure were investigated. The P Complex, initiator and PI were characterized by GPC, 1H NMR and 7Li NMR. Results showed that there only existed an acceleratory point of inflexion in the conversion time curve instead of the stationary conversion platform when the polymerization temperature was much higher than PI’s glass transition temperature. Same queries in the anionic polymerization theory which could hardly be understood before being explained with the new hypothesis proposed recently. The aggregated initiator can initiate the anionic polymerization and confine the aggregated supramolecules, but they will disintegrate thoroughly during the following polymerization. Furthermore, the polymer structure can be controlled by changing the distance between ion pairs. When P Complex was added in the polymerization system initiated by n BuLi, the reaction was intensified because the lithium was shared by both P Complex and n BuLi. Therefore, the content of poly 3, 4 isoprene increased to more than 50% in the polymerization since the interspace between the ion pairs was blocked by P Complex with big bulk.