The present invention relates to a phosphine-functionalized polyether imidazolium-based ionic liquid and a method for biphasic hydroformaylation of olefins based on the phosphine-functionalized polyether imidazolium-based ionic liquid. The method uses a biphasic catalytic system, wherein the catalytic system consists of a phosphine functionalized polyether imidazolium-based ionic liquid, a rhodium catalyst, the reaction substrate, olefins and the reaction product, aldehydes; liquid/liquid biphasic hydroformylation of olefins is performed at a certain reaction temperature and syngas pressure; the phosphine-functionalized polyether imidazolium-based ionic liquid acts both as a phosphine ligand and as a rhodium catalyst carrier; there is no need to add any other ionic liquid to the system; and separation and recycle of the rhodium catalyst are realized by liquid/liquid biphasic separation after the reaction. The catalytic system provided by the present invention is high in catalytic activity. The rhodium catalyst is capable of being recycled for many times with no obvious decrease in catalytic activity and selectivity.