The invention provides a graphite condenser for a gas boiler and a preparation method for the graphite condenser. The graphite condenser for the gas boiler is installed on a flue in front of a gas boiler chimney. The graphite condenser comprises a support device and a graphite condensing device supported and located on the support device. The graphite condensing device comprises at least one graphite condensing unit. The graphite condensing unit comprises a square graphite condensing block, an upper cover plate, a lower bottom plate, an upper seal plate, a lower seal plate, a left side plate,a right side plate, a front side plate, a rear side plate, a front seal plate and a rear seal plate. The graphite condensing block is provided with multiple lines of up-down-through smoke communicating holes and front-back-through circulating water communicating holes, and the smoke communicating holes do not communicate with the circulating water communicating holes. The upper cover plate is provided with a smoke inlet. The lower bottom plate is provided with a smoke outlet. The lower portion of the front side plate is provided with a circulating water inlet. The upper portion of the rear side plate is provided with a circulating water outlet. The graphite condenser provided by the invention is high in heat exchange efficiency and capable of recycling a large amount of smoke water heat, and the problem of low-temperature corrosion can be solved completely due to properties of materials.