The invention relates to a polymerization method for producing solution polymerized butadiene-isoprene rubber. The polymerization method comprises the following steps of: copolymerizing butadiene and isoprene in a hydrocarbon solvent at 0-130 DEG C in the presence of organic lithium as an initiator and tetrahydrofurfuryl alcohol as a structure regulator and after polymerization reaction basically completes, adding a coupling agent with functionality of 2-4 into the copolymer to perform the coupling reaction. The tetrahydrofurfuryl alcohol is used as the structure regulator, so as to obtain a 1,2-structure content adjustable random copolymer rubber.