Photoelectron velocity-map imaging spectroscopy was conducted for the heterotrinuclear metal carbonyls V2Ni(CO)n- (n = 6-10). Electronic structure calculations were performed to understand the experimental spectral features. The binding motif of a V-V-Ni chain with two side-on-bonded carbonyls and two bridging carbonyls is favored in the n = 6-9 clusters. A V2Ni triangle core structure is formed at n = 10 with the involvement of two carbonyls with the carbon atom triply coordinated to metal atoms, three bridging carbonyls, and five terminal carbonyls, in which CO bonding configurations mirror the adsorption features in the three-fold hollow, bridging, and atop sites on the closely packed surface, respectively. The present study provides a stepwise picture for molecular level understanding of CO bonding on heteronuclear metal clusters, which is directly relevant to the elementary processes of CO on the alloy surfaces/interfaces.