In this paper, we present a statistical study of the [C ii] 158 mu m line and the CO(1-0) emission for a sample of similar to 200 local and high-z (32 sources with z > 1) galaxies with very different physical conditions. We explore the correlation between the luminosities of [C ii] and CO(1-0) lines and obtain a strong linear relationship, confirming that [C ii] is able to trace total molecular gas mass, with a small difference between (U)LIRGs and less-luminous galaxies. The tight and linear relation between [C ii] and CO(1-0) is likely determined by the average value of the observed visual extinction A(V) and the range of G(0)/n in galaxies. Further investigations into the dependence of L-[C ii]/LCO(1-0) on different physical properties show that L-[C ii]/LCO(1-0) (1) anticorrelates with Sigma(IR), and the correlation becomes steeper when Sigma(IR) greater than or similar to 10(11)L(circle dot) kpc(-2); (2) correlates positively with the distance from the main sequence Delta(MS) when Delta(MS) less than or similar to 0; and (3) tends to show a systematically smaller value in systems where the [C ii] emission is dominated by ionized gas. Our results imply that caution needs to be taken when applying a constant [C ii]-to-M-mol conversion factor to estimate the molecular gas content in extreme cases, such as galaxies having low-level star formation activity or high star formation rate surface density.