7. The sequence $\left\{a_{n}\right\}$ satisfies:
$$
\begin{array}{l}
a_{1}=0, a_{2}=1, \\
a_{n+1}=\frac{\sqrt{6}-\sqrt{2}}{2} a_{n}-a_{n-1}(n \geqslant 2) .
\end{array}
$$

Then $a_{2019}=$
7. $\frac{\sqrt{6}-\sqrt{2}}{2}$.

Solve the characteristic equation
$$
\begin{array}{l}
x^{2}-\frac{\sqrt{6}-\sqrt{2}}{2} x+1=0 \\
\Rightarrow x_{1,2}=\frac{\sqrt{6}-\sqrt{2}}{4} \pm \frac{\sqrt{6}+\sqrt{2}}{2} \mathrm{i} \\
=\cos \frac{5 \pi}{12} \pm \mathrm{i} \sin \frac{5 \pi}{12} .
\end{array}
$$

Therefore, $\left\{a_{n}\right\}$ is a sequence with a period of 24.
Thus, $a_{2019}=a_{3}=\frac{\sqrt{6}-\sqrt{2}}{2}$.