NOVELTY - Rectifying for preparing high pure gas comprises: (1) preparing target gas raw material into the dehydration, the light constituent removing tower top gas discharged by the tower top condenser, a condensing liquid back to the dehydration as reflux liquid from the tower top, condensing the light component impurities, stream is discharged, the light material into heavy, heavy tower top gas from the purifying, tower kettle discharging heavy component impurities stream; (2) using cooling medium and the heat exchange of the condenser heavy tower; and (3) dividing into three parts.    USE - The method is useful for rectifying for preparing high pure gas. The high-purity gas is useful for electronic industry with high purity gas; and for high pure hydrogen chloride gas for electronic industry, electronic industry with high purity chlorine or electronic industry with high-purity ammonia (all claimed).    ADVANTAGE - The method or system device is simple, energy saving, and has flexible operation and wide application, where it is easy to maintain.    DETAILED DESCRIPTION - Rectifying for preparing high pure gas comprises: (1) preparing target gas raw material into the dehydration, the light constituent removing tower top gas discharged by the tower top condenser, a condensing liquid back to the dehydration as reflux liquid from the tower top, condensing the light component impurities, stream is discharged, the light material into heavy, heavy tower top gas from the purifying, tower kettle discharging heavy component impurities stream; (2) using cooling medium and the heat exchange of the condenser heavy tower; and (3) dividing into three parts, the first part of the liquid is used as the cooling medium of the dehydration tower top condenser through the throttle expansion, the second part as reflux liquid of the constituent through the throttle expansion, and the third part is used as product. An INDEPENDENT CLAIM is a system comprising unit for dehydration, for removing the target gas in the raw material of the light component impurities, a dehydration tower top condenser, which is used for making the light-constituent removing tower top cooling condensation exhaust gas, a constituent for the heavy component impurities in the material to remove the light is, a compressor is used for the top condenser heat exchange through the dehydration tower of the cooling medium and the heavy tower top purifying gas combined into compressed gas, heat the first part and light constituent removing tower material is a light-constituent removing tower and boiling for the compressed gas, a heavy tower re-boiling device, which is used for the compressed gas to the second portion of the de-heavy tower material of the receipt, a liquid storage tank for storing at least the compressed gas of the first part and the second part of the condensed liquid, a first throttle valve, which is used for the liquid in the tank a portion of the liquid to carry out flow expansion as the cooling medium of the dehydration tower top condenser, a second throttle valve, which is used for the liquid in the tank the second portion of the liquid to carry out flow expansion, as reflux liquid of the constituent, the liquid storage tank is connected with a product line for the liquid in the tank liquid of the third part is used as product.