Time-dependent Flow characteristics of a two-dimensional lid-driven square cavity flow of six high Reynolds numbers, $10^4 2{ imes}lO^4., 3{ imes}l0^4, 5{ imes}lO^4, 7.5{ imes}lO^4$ and $10^5$ were investigated. A convection conservative difference scheme based upon SOLA to maintain the nearly 2nd-order spatial accuracy was adopted on irregular grid formation. Irregular grid number is $80{ imes}80$ and its minimum size is about 1/400 of the cavity height(H) and its maximum is about 1/53 H. The result shows that at Re= $10^4$, periodic migration of small eddies appearing in corner separation region and its temporal sinusoidal fluctuation are represented. And another critical Reynolds number which shows the commencement of flow randomness emerging from the periodic fluctuation is assumed to be around Re= $1.5{ imes}10$. At five higher Reynolds numbers ($2{ imes}lO^4., 3{ imes}l0^4, 5{ imes}lO^4, 7.5{ imes}lO^4$ and $10^5$), an organizing structure of four consecutive vortices similar to a Moffat vortex at two lower corners is revealed from time-mean flow patterns.