Provided is a graphite material for a heat exchanger. The graphite material is mainly prepared by mixing pitch meso-carbon microbeads, a petroleum coke stage material and modified pitch, wherein the petroleum coke stage material is needle petroleum coke subjected to secondary coking or third-time coking. A preparation method comprises the steps that the petroleum coke and modified pitch slurry are subjected to mixing kneading and rolling and flaking under vacuum condition, cooling and smashing are conducted in sequence, the smashed materials are subjected to mixing, standing, isostatic press molding, calcining and smashing, and the petroleum coke stage material is obtained; the petroleum coke stage material and the pitch meso-carbon microbeads are subjected to mixing kneading, the modified pitch is added and rolled to be flakes, cooling and smashing are conducted in sequence, the smashed materials are subject to mixing, standing, isostatic press molding, calcining carbonization treatment and graphitization treatment, and the graphite material for the heat exchanger is obtained. According to the graphite material for the heat exchanger, the needle petroleum coke subjected to secondary coking or third-time coking is used for the first time, toughness and self-lubrication of graphite are enhanced, the processing efficiency of graphite machinery is improved, and thermal conductivity of graphite pieces can be increased.