The utility model relates to the technical field of a pretreatment device used before chemical sample analysis and discloses a copper ion on-line analysis pretreatment device, wherein a storage device for a sample to be analyzed is connected with a feeding hole of a first metering pump, and a discharge hole of the first metering pump is connected with one feeding hole of a masking reactor by a second switch valve; another feeding hole of the masking reactor is connected with a discharge hole of a second metering pump by a first switch valve; a feeding hole of the second metering pump is connected with a masking reactant storage device; a discharge hole of the masking reactor is connected with a feeding hole of a filtering mechanism; a discharge hole of the filtering mechanism is connected with a copper ion analysis device by a fourth switch valve. The on-line analysis pretreatment device also has a reverse cleaning function. According to the device, the electrolyte sample to be analyzed is pretreated before the on-line analysis of the copper ions, so that interfering ions and other impurities can be effectively removed, the analysis result is more accurate, and powerful data guidance is provided for the follow-up work.