Abstract: The gas phase reaction of Cu plasma and acetonitrile clusters is studied by the laser ablation-molecular beam（LAMB） method. Four series of clustered complex ions Cu+（CH3CN）n， CH2CN+（CH3CN）n，H+（CH3CN）n and CH3CHCN+（CH3CN）n are observed. Interestingly，the species and sizes of the product clusters vary observably when the plasma acts on the different parts of the pulsed acetonitrile molecular beam. When the laser ablated Cu plasma acts on the head of the beam，the metal acetonitrile complex clusters Cu+（CH3CN）n together with protonated acetonitrile clusters H+（CH3CN）n and deprotonated acetonitrile clusters CH2CN+ （CH3CN）n are domain，while the plasma acts on the middle of the beam. However，CH2CN+（CH3CN）n and H+（CH3CN）n along with the clusters CH3CHCN+（CH3CN）n turn out to be the main resulting clusters. By comparing the intensities and the cluster sizes of CH3CHCN+（CH3CN）n with H+（CH3CN）n and CH2CN+（CH3CN）n，the formation of CH3CHCN +（CH3CN）n is contributed to the intracluster ion-molecule reaction of acetonitrile clusters.