V-51 NMR was used as a new pseudo in situ and nondestructive analytical tool to monitor and identify possible products of [VS4-Cu-n] (n less than or equal to 6) clusters. The reaction of (NH4)(3)VS4/Et4NBr/CuBr/PPh3 systems with various molar ratios in CH2Cl2 were mimicked in NMR tubes. The reaction conditions for the formation of the [VS4-Cu-n] clusters with different coordinate number of copper atoms n were studied. The results show the influence of the ratio among the reactants on the products and reveal the reaction mechanism in solution. This method not only provides some information about reaction mechanism, but also provides a guide in the synthesis of some clusters such as V-Cu-S clusters with less or more coordinate copper number whose reaction conditions (solvent, temperature, pH etc,) are difficult to be determined.