The invention relates to a system and method for improving the heat exchange effects of graphite blocks in an HCl synthetic furnace with byproduct steam. The method comprises the steps that water in a first water tank enters the lower end of a circulating water section of a synthetic furnace after undergoing heat exchange in a heat exchanger, then comes out from the upper end of the circulating water section of the synthetic furnace and returns to the first water tank; hot water in the middle of the circulating water section of the synthetic furnace enters a second water tank, and the hot water in the second water tank returns to the synthetic furnace and generates low-pressure steam under the pressurization action of a first water pump. The system and the method have the beneficial technical effects that the water in the second water tank comes from the middle section of the circulating water in the synthetic furnace and has higher temperature, and the hot water enters the synthetic furnace to generate steam under the pressure of the first water pump, thus effectively utilizing the heat in the circulating water and saving the extra heating cost; pure water is used instead of original industrial water and contains little calcium and magnesium ions and silt, so that scaling and blockage are avoided, thus prolonging the service life of equipment and then greatly reducing the accident danger coefficient and reducing the installation and maintenance costs of the equipment.