设向量overrightarrow(a)与向量overrightarrow(b)= ( (2,-1,2) )平行，并满足等式overrightarrow(a)cdot overrightarrow(b)=-18，则overrightarrow(a)=_ _ _ _ _ _ _ _ _ _ .

$\because \overrightarrow{a}\parallel \overrightarrow{b}$

$\therefore $设$\overrightarrow{a}=k\overrightarrow{b}$

$\because \overrightarrow{b}=\left ( {2,-1,2} \right )$

$\therefore \overrightarrow{a}=k\left ( {2,-1,2} \right )$

$=\left ( {2k,-k,2k} \right )$

$\because \overrightarrow{a}\cdot \overrightarrow{b}=-18$

$\therefore 2\times 2k+\left ( {-1} \right )\times \left ( {-k} \right )+2\times 2k=-18$

解得$k=-2$

$\therefore \overrightarrow{a}=\left ( {-4,2,-4} \right )$

综上所述，答案：$\left ( {-4,2,-4} \right )$