Nitrogen mainly exists as nitrate in aqueous environments. In karst areas, nitrate pollution caused by anthropogenic activities severely endangers aqueous systems. In order to identify nitrate sources, nitrate in the cave water of Mahuang Cave was comprehensively analysed using hydrochemistry, delta 15N-delta 18O isotopes and stable isotope analysis in R. The results indicate that the nitrate content in the cave water presented insignificant seasonal variations but significant spatial variations. Compared with the variation of delta 15N-NO3-, the seasonal variation of delta 18O-NO3- was positive (2.68 parts per thousand) in the dry season and negative (-0.52 parts per thousand) in the wet season. The variation of NO3- and Cl- and the isotopes of NO3- (delta 15N, delta 18O) suggest multiple sources of NO3- in the water. The average contribution of different nitrate sources in the karst cave water was assessed by the SIAR model: chemical fertilisers (46.29%) > soil nitrogen (30.57%) > manure & sewage (14.14%) > atmospheric precipitation (9.14%) in the dry season and chemical fertilisers (61.86%) > soil nitrogen (20.29%) > manure & sewage (12.43%) > atmospheric precipitation(5.57%) in the wet season. The contribution in dry and wet seasons was dominated by chemical fertilisers and soil nitrogen.