We present a statistical study on the [C I]($^{3} rm P_{1} rightarrow {rm ^3 P}_{0}$), [C I] ($^{3} rm P_{2} rightarrow {rm ^3 P}_{1}$) lines (hereafter [C I] (1$-$0) and [C I] (2$-$1), respectively) and the CO (1$-$0) line for a sample of (ultra)luminous infrared galaxies [(U)LIRGs]. We explore the correlations between the luminosities of CO (1$-$0) and [C I] lines, and find that $L_mathrm{CO(1-0)}$ correlates almost linearly with both $L_ mathrm{[CI](1-0)}$ and $L_mathrm{[CI](2-1)}$, suggesting that [C I] lines can trace total molecular gas mass at least for (U)LIRGs. We also investigate the dependence of $L_mathrm{[CI](1-0)}$/$L_mathrm{CO(1-0)}$, $L_mathrm{[CI](2-1)}$/$L_mathrm{CO(1-0)}$ and $L_mathrm{[CI](2-1)}$/$L_mathrm{[CI](1-0)}$ on the far-infrared color of 60-to-100 $mu$m, and find non-correlation, a weak correlation and a modest correlation, respectively. Under the assumption that these two carbon transitions are optically thin, we further calculate the [C I] line excitation temperatures, atomic carbon masses, and the mean [C I] line flux-to-H$_2$ mass conversion factors for our sample. The resulting $mathrm{H_2}$ masses using these [C I]-based conversion factors roughly agree with those derived from $L_mathrm{CO(1-0)}$ and CO-to-H$_2$ conversion factor.
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