The invention discloses an asphalt core wall base and a construction method thereof. By adopting the asphalt core wall base and the construction method thereof, the problem that an original earth-rock dam cannot be used for overflowing in the filling process is solved. The asphalt core wall base comprises a base foundation surface and a base body. The base foundation surface is arranged on a base rock. The base body is arranged on the base foundation surface. The horizontal height of the top of the base body is larger than that of a dam body foundation surface. The method is applied to construction of the asphalt core wall base. The horizontal height of the top of the base body in the base is larger than that of the dam body foundation surface, so the portion, higher than the dam body foundation surface, of the base can protect safety of a fracture surface on the lower portion of a dam body, and the earth-rock dam can conduct overflowing in the filling process; moreover, the height of a cofferdam arranged on the upper stream is reduced, the number of diversion tunnels is reduced, investment is saved, the construction period is shortened, and the layout of a hydro-project is optimized.