A backfilling-type online chromatographic detector for sulphur hexafluoride decomposition products includes: a compression pump, a vacuum pump, a gas storage tank, a first six-way valve, a second six-way valve, a first chromatographic column, a second chromatographic column and a detector. One end of the compression pump is connected to one end of the vacuum pump, another end of the vacuum pump is connected to one end of the gas storage tank, another end of the gas storage tank is connected to the first chromatographic column through the first six-way valve, the first chromatographic column is connected to the second chromatographic column through the second six-way valve, and the second chromatographic column is connected to the detector.