The potential energy surface (PES) for the isomerizations and dissociations of the acrylonitrile radical cation was determined from the CBS-QB3 and CBS-APNO calculations. The Rice-Ramsperger-Kassel-Marcus model calculations were performed based on the PES in order to predict the competitions among the dissociation channels. The mechanisms for the loss of $H^{ullet}$, $H_2$, $CN^{ullet}$, HCN, and HNC were proposed. The $C_3H_2N^+$ ion formed by loss of $H^{ullet}$ was predicted as a mixture of $CH{equiv}C-C=NH^+$, $CH{equiv}C-N{equiv}CH^+$, and $CH_2=C-C{equiv}N^+$. Furthermore $CH{equiv}C-C{equiv}N^{+{ullet}}$ was formed mainly by a consecutive 1,2-H shift and 1,2-H2 elimination.