  Using operators' Weyl ordering expansion formula (Hong-yi Fan,\emph{\}J.
Phys. A 25 (1992) 3443) we find new two-fold integration transformation about
the Wigner operator $\Delta(q',p')$ ($q$-number transform) in phase space
quantum mechanics, \[ \iint_{-\infty}^\infty dp' dq'/\pi \Delta (q',p')
e^{-2i(p-p') (q-q')} =\delta (p-P) \delta (q-Q), \] and its inverse
\[\iint_{-\infty}^\infty dq dp \delta (p-P) \delta (q-Q) e^{2i(p-p')
(q-q')}=\Delta (q',p'), \] where $Q,$ $P$ are the coordinate and momentum
operators, respectively. We apply it to studying mutual converting formulas
among $Q-P$ ordering, $P-Q$ ordering and Weyl ordering of operators. In this
way, the contents of phase space quantum mechanics can be enriched.
