  The coincidence problem is studied for the dark energy model of effective
Yang-Mills condensate in a flat expanding universe during the matter-dominated
stage. The YMC energy $\rho_y(t)$ is taken to represent the dark energy, which
is coupled either with the matter, or with both the matter and the radiation
components. The effective YM Lagrangian is completely determined by quantum
field theory up to 1-loop order. It is found that under very generic initial
conditions and for a variety of forms of coupling, the existence of the scaling
solution during the early stages and the subsequent exit from the scaling
regime are inevitable. The transition to the accelerating stage always occurs
around a redshift $z\simeq (0.3\sim 0.5)$. Moreover, when the Yang-Mills
condensate transfers energy into matter or into both matter and radiation, the
equation of state $w_y$ of the Yang-Mills condensate can cross over -1 around
$z\sim 2$, and takes on a current value $\simeq -1.1$. This is consistent with
the recent preliminary observations on supernovae Ia. Therefore, the
coincidence problem can be naturally solved in the effective YMC dark energy
models.
