Rich soft X-ray emission lines of highly charged silicon ions (Si VI--Si XII) were observed by irradiating an ultra-intense laser pulse with width of 200 fs and energy of $sim$90 mJ on the solid silicon target. The high resolution spectra of highly charged silicon ions with full-width at half maximum (FWHM) of $sim$0.3--0.4AA is analyzed in wavelength range of 40--90 AA . The wavelengths of 53 prominent lines are determined with statistical uncertainties being up to 0.005 AA . Collisional-radiative models were constructed for Si VI -- Si XII ions, which satisfactorily reproduces the experimental spectra, and helps the line identification. Calculations at different electron densities reveal that the spectra of dense plasmas are more complicate than the spectra of thin plasmas. A comparison with the Kelly database reveals a good agreement for most peak intensities, and differences for a few emission lines.
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