We present new data on Cherenkov light observations obtained during 1994–2009 period, after a modernization of the Yakutsk EAS array. A complex analysis of <i>x</i><sub>max</sub> and its fluctuations σ(<i>x</i><sub>max</sub>) was performed in a wide energy range. With the new data, according to QGSJet II model, an estimation was made of cosmic rays mass composition for <i>E</i><sub>0</sub>~10<sup>17</sup>–3×10<sup>19</sup> eV. The result points towards a mixed composition with a large portion of heavy nuclei at <i>E</i><sub>0</sub>~10<sup>17</sup> eV and the dominance of light nuclei at <i>E</i><sub>0</sub>~10<sup>19</sup> eV. The analysis of σ<i>x</i><sub>max</sub> energy dependence for the same energies qualitatively confirms this result. A shape of <i>x</i><sub>max</sub> distribution at fixed energy 10<sup>18</sup> eV is analysed to make more precise conclusion on cosmic ray mass composition.