So far, separation and scale production of high-purity semiconducting single-walled carbon nanotubes (s-SWNTs) remains one of the foremost hurdles in SWNT applications. N, N-bis (2-hydroxyethyl) dodecanamide (DDA), a kind of nonionic alkanolamide surfactant with a p-conjugated amide group, exhibits strong selectivity for s-SWNTs within a certain diameter range by constructing a specific oil/water bi-continuous system. It was found that the amide groups of DDA molecules showed specific recognition ability to s-SWNTs by electrostatic complementarity in nonpolar medium, while the diameter selectivity resulted from the different adsorption geometries of the alkyl chains of DDA molecules on s-SWNTs under hydrophobic interaction in the constructed oil/water bi-continuous system. The high yield (similar to 33.6%) of the sorted s-SWNTs benefited from the precision of the self-assembly behavior of surfactant molecules. The finding in this work not only is meaningful for paving a way to selectively separate s-SWNTs in large scale with low-cost, but also reveals one kind of critical interaction between amide groups and s-SWNTs, which may be an essential point influencing the exploitation of the potential applications of s-SWNTs in many fields.