The invention discloses a horizontal continuous casting graphite crystallizer, which comprises an outer sleeve body and an inner core; the tail end of the inner core is connected with the rear end ofthe outer sleeve body; a ring-shaped channel is arranged between the inner core and the outer sleeve body; a liquid inlet which is communicated with the ring-shaped channel is formed on the bottom wall of the rear end of the inner core; the shaft part of the inner core includes a first action part and a second action part, which are connected in sequence from the tail end of the shaft part to thefront end thereof; the cone angle Alfa of the first action part is larger than the cone angle Beta of the second action part; and the ratio of the cone angle Alfa to the cone angle Beta is equal to orlarger than 2.5. The connecting part between the first action part and the second action part is smooth transition. Copper roughcasts continuously cast by the continuous casting graphite crystallizerhave smooth inner surfaces without crystal lines, thus improving the shaping quality of roughcasts, eliminating hidden quality troubles, and being favorable for further deep processing for shaping.