<p>In this study, a silicon-bridged diphosphine/CrCl₃(C₄H₈O)₃/modified methylaluminoxane catalytic system (PNSiP/CrCl₃(THF)₃/MMAO) was constructed, to explore the possibility of producing high-carbon olefins via ethylene/light <i>α</i>-olefins co-oligomerization. The choice of <i>α</i>-olefin monomer, ethylene pressure, and reaction temperature played crucial roles in determining the distribution of products. In presence of ethylene and 1-hexene, the primary high-carbon products are C₁₀ olefins. In contrast, when ethylene and 1-octene are present, the main high-carbon products are C₁₂ olefins. Increasing temperature and reducing pressure can promote the oligomerization of <i>α</i>-olefins with ethylene, thereby significantly improving the selectivity of high-carbon products. Detailed identities of C₁₀-C₁₄ olefins, assigned by gas chromatographic and mass spectrometric, strongly supported a mechanism involves five-, seven- and nine-membered metallacyclic intermediates composed by ethylene and <i>α</i>-olefins units. Mechanistic analysis of C₁₂ and C₁₄ isomers revealed that co-trimerization and co-tetramerization reactions occurred concurrently during the reaction process. Furthermore, the concentration of specific carbon-number olefins, along with the reaction conditions, influenced the relative probability of the two pathways.</p> Graphical abstract <p></p>