The invention relates to a method for modifying a polybutadiene-styrene random active lithium polymer by using unsaturated epoxidized polysiloxane. The unsaturated epoxidized polysiloxane provided bythe invention contains unsaturated double bonds and a plurality of epoxy groups with relatively high activity, and contains no active silicon-hydrogen bonds, and a coupling reaction or an end cappingreaction can be effectively carried out on the epoxy groups with active lithium at the tail end of the styrene-butadiene random copolymer, so that multifunctional solution-polymerized styrene-butadiene rubber is obtained. When raw rubber of the multifunctional solution-polymerized styrene-butadiene rubber (SSBR) is used as tread rubber of radial semi-steel tires, the tread vulcanized rubber has relatively low dynamic heat generation, and meanwhile, the rolling resistance reduction rate reaches 28% or above.