Abstract: The superpositional interference resulted from the ions of carbide andoxide of barium and rare earths causes significant errors in determining REtrace by spark source mass spectrometry when graphite is used as conductivepowder. In the present paper a mathematial correction procedure, whicheliminates the interference by using a coupled equation for intensity of singleexposure, is described. Its reliability has been verified by more than 20Chinese geological standard samples.