We investigated IPv and IPa for a series of SWCNTs as functions of the tube length by means of the DFT. Our calculations revealed that SWCNTs length, changing the local aromaticity periodically, affects their IPs values. Whereas “short” tubes demonstrate notable gap between IPv and IPa, “long” SWCNTs, for example C200H20, have similar IPv and IPa. It looks very possible, that in the case of real SWCNTs the both types of IPs become equal. It was established, that lengths of studied SWCNTs undergo a change upon ionization, and in the case of “short” tubes these relative changes are significant. This interesting effect of elongation or shortening, most probably, depends on the HOMO electron density distribution in SWCNTs.