Abstract: Decomposition products of sulfur hexafluoride (SF₆) are essential markers of faults in SF₆ gas insulated equipment. A portable time-of-flight mass spectrometer (TOF MS) was designed to achieve fast and accurate quantification of several decomposition products of SF₆ in situ, so as to provide crucial information for condition assessment and fault diagnosis of SF₆ gas insulated equipment. Characterized by a pulse sampling design, gas samples in SF₆ gas insulated equipment could be directly introduced into the TOF MS and analyzed without removal of the equipment from service. With a total volume of 20 mL of the pulse sampling pipeline and a sampling flow rate under 1 mL/min, less than 35 mL (under 1 atm) gas sample was required per test, representing a reduction over 85% in sample consumption compared with previous TOF MS design. Additionally, the new pulse sampling design showed a cleaner background signal. The detection sensitivity for four typical decomposition products of SF₆, i.e. SO₂F₂, SO₂, CS₂, CF₄, was determined to be 5 μL/L or better. The performance of the portable TOF MS was evaluated in recent field work, confirming its value in condition assessment and fault diagnosis of SF₆ gas insulated equipment and showing a broad application prospect in power industry.