NOVELTY - Preparing n-butane by using isobutane comprises e.g. providing feeding gas flow A containing at least 80% isobutane, feeding the feeding gas flow A into at least one n-structured zone and enabling isobutane to have n-merization reaction in presence of a catalyst to obtain a product gas flow B, feeding the product gas flow B into at least one hydrogenation saturation zone, and hydrogenating isobutylene, 1-butene, 2-butene and propylene to obtain a gas flow C, carrying out condensing separation on the gas flow C to obtain a gas phase flow d1 and a liquid phase flow d2.    USE - The method is useful for preparing n-butane by using isobutane (claimed).    ADVANTAGE - The method: is simple and controllable; and has high conversion rate, high yield and good economical benefits.    DETAILED DESCRIPTION - Preparing n-butane by using isobutane comprises (a) providing feeding gas flow A containing at least 80% isobutane, (b) feeding the feeding gas flow A into at least one n-structured zone and enabling isobutane to have n-merization reaction in presence of a catalyst to obtain a product gas flow B containing isobutane, n-butane, methane, ethane, propane, propylene, isobutylene, 1-butene, 2-butene and hydrogen, (c) feeding the product gas flow B into at least one hydrogenation saturation zone, and hydrogenating isobutylene, 1-butene, 2-butene and propylene to obtain a gas flow C containing isobutane, n-butane, methane, ethane, propane and hydrogen, (d) carrying out condensing separation on the gas flow C at 0-40 degrees C to obtain a gas phase flow d1 containing hydrogen, methane, ethane, propane and other low-boiling secondary components, and a liquid phase flow d2 containing methane, ethane, propane, n-butane and isobutane, (e) feeding the liquid phase flow d2 into a first distillation zone to separate low-boiling-point secondary components in the liquid phase flow d2 to form a product flow e1 containing methane, ethane, propane and isobutane, and product flow e2 containing isobutane and n-butane, and (f) feeding the product flow e2 into a second distillation zone for separating isobutane and n-butane to obtain isobutane flow f1 and n-butane flow f2, and recycling isobutane flow f1 into the n-structured zone.