Abstract: The probe is usually corroded by chemical solutions in permittivity measurements. An apparatus which realizes wide-band online non-contact measurement is proposed to resolve this problem. S-parameters are obtained by full-wave simulations with the proposed coaxial apparatus to reconstruct the permittivities of several solutions. Moreover, the effective permittivities are achieved by means of genetic algorithm (GA) under prearranged measurement errors of 2%. The reconstructed results of the effective permittivies of chemical solutions agree well with previously published data with relative errors of less than 5%, showing the coaxial apparatus’ obvious advantages over conventional apparatuses.