Effective Potential of QCD

We present a simple method to calculate the one-loop effective action of QCD which reduces the calculation to that of SU(2) QCD. For the chromomagnetic background we show that the effective potential has an absolute minimum only when two color magnetic fields $H_{\mu\nu}^3$ and $H_{\mu\nu}^8$ are orthogonal to each other. For the chromoelectric background we find that the imaginary part of the effective action has a negative signature, which implies the gluon pair-annihilation. We discuss the physical implications of our result.