Linear α-olefins are important chemical raw materials. Selective oligomerization of ethylene to produce α-olefins with specific carbon numbers has become an important development direction in the future. PNP-type ligands were extensively studied in the reaction of chromium-catalyzed selective oligomerization of ethylene to produce α-olefins. Due to the structural characteristics, multi-site PNP ligands may form unique coordination mode in the process of coordination with chromium center, thus affecting the catalytic performance. In this paper, the application of PNP ligands with multi-nuclear PNP ligands, N and P atoms with N, S or O heteroatoms in ethylene selective oligomerization was reviewed.