Carbon cluster anionsare generated by a standard laser vaporization/pulsed molecular beam scheme and detectedwith a time of flight mass spectrometer. Through the study of mass spectra, it is revealedthat the structure of most carbon clusters transforms from rings to cages as the clustersize grows up. The discussion is focussed on how the intensities of the vaporizing laserand carrier gas influence the characteristics of the C-n massspectra.