In this paper，the qualitative and semi -quantitative analysis of polysulfide speciesdissolved in electrolyte during the discharge -charge process and cycling of Li - S batteries wasreported. ICP - OES (Inductively coupled plasma -Optical emission spectrometer) measurement was usedto estimate the total sulfur dissolved inelectrolyte. Polysulfide with different ordered wereseparated and confirmed by LC - MS (Liquidchromatography coupled with mass spectrometry). Li2S4and Li2S6 were proved to be the most stable form ofpolysulfide species. At the end of discharge process,total sulfur in the form of Ii2S4 and Li2S6 remainedin electrolyte about 20% . At the end of chargeprocess，45% active material was preserved inelectrolyte mainly in the form of Li2S6. The partialtransformation of active material from liquid phaseto solid phase resulted in the practical specificcapacity lower than theoretical capacity. In cyclesactive material transferred between liquid and solidphase kept a balance，the content of total sulfur,Li2S4 and Li2S6 were changed slightly at the end ofcycles. Consequently，polysulfide dissolved inelectrolyte just took limited responsibility for thecapacity fading with cycles of Li - S batteries.
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