A reaction method and catalyst for long-chain internal olefin isomerization and hydroformylation, adopting two metal complexes of rhodium and ruthenium as catalysts, and further adopting a tridentate phosphorus ligand. The catalytic system can perform a homogeneous internal olefin isomerization and hydroformylation reaction under a certain temperature and pressure to obtain an aldehyde product with a high normal-to-iso ratio. The method is suitable for a long-chain internal olefin (>C8), and is also suitable for an internal olefin with less than 8 carbons.