Midfielders Deng Zhuoxiang and Yu Hanchao scored twice, with Qu Bo and Yang Xu also finding the net for the visitors, while Visay Phapouvanin scored for Laos.
The result moved China into the third-round group stage, when the region’s powers including Japan, South Korea and Australia will enter the competition.
China’s comfortable margin of victory over two legs came after Laos had taken a shock 2-0 lead in last weekend’s away leg, before being overwhelmed 7-2.