The single electron capture cross sections for 5-30keV Ho+, La+ and Ce+ impact on H2 at a fixed anode voltage of an ion source and 10keV Ho+ impact on H2 at different anode voltage have been measured by the “growth rate method”. We found that the variation of the hollow cathode ion source’s anode voltage affected the proportion of the metastable states of the rare earth ions, and the proportion accounts for the significant change of single capture cross sections.