The invention discloses an isoquinoline derivant. The said derivant, with 9,10-dimethoxy -[1,3] dioxide [4,5-g] isoquinoline [3,2-a] isoquinoline -7-ylidehydrochlorate (I) as its representative, reduces plasma cholesterol level by massively absorbing low density lipoprotein cholesterol and changing them to bile acid in liver. The 9,10-dimethoxy -[1,3] dioxide [4,5-g] isoquinoline [3,2-a] isoquinoline-7-ylidehydrochlorate is a new cholesterol lowering compound which is different in cholesterol lowering mechanism from statins. The 9,10-dimethoxy -[1,3] dioxide [4,5-g] isoquinoline [3,2-a] isoquinoline -7-ylidehydrochlorate and other isoquinoline derivants have an extremely low side toxiceffect, so they are safe natural cholesterol lowering compounds.