The invention belongs to the technical field of pavement materials, in particular to a high-viscosity asphalt modifier soluble in asphalt and a production method thereof. The modifier contains SBS (styrene-butadiene block copolymer), petroleum resin, aromatic oil, an antioxidant, a lubricating agent, a grafting agent and an initiating agent; the materials enter a reciprocating screw extruder and a single-screw extruder by an automatic weighing system through an automatic weighing system, are mixed, cut and extruded at the temperature of 100-190 DEG C, then are granulated by an underwater granulator and are packaged by an automatic weighing and packaging machine after being cooled, centrifugally dehydrated, sieved and dried. The production method has convenient process operation, high product yield, high product percent of pass and no pollution discharge, and the modifier is easy to dissolve in the asphalt. The modifier can be directly mixed with the asphalt to be stirred to prepare the high-viscosity asphalt and has very convenient use; moreover, the performance of the modifier completely meets the technical requirements.