Titan is the largest satellite of Saturn. In its atmosphere, CH4 is the most abundant neutral after nitrogen. In this paper, the complex doublet potential-energy surface related to the reaction between, HCN+ and CH4 is investigated at the B3LYP/6-311G(d,p), CCSD(T)/6-311G++(3df,2pd)(single-point), and QCISD/6-311G(d,p) computational levels. A total of seven products are located on the PES. The initial association of HCN+ with CH4 is found to be a prereaction complex 1 (HCNHCH3+) without barrier. Starting from 1, the most feasible pathway is the direct H-abstraction process (the internal C-H bond dissociation) leading to the product P-1 (HCNH++CH3). By C-C addition, prereaction complex 1 can form intermediate 2 (HNCHCH3+) and then lead to the product P-2 (CH3CNH++H). The rate-controlling step of this process is only 25.6 kcal/mol. It makes the Path P-2 (1) R -> 1 -> TS1/2 -> 2 -> TS2/P-2 -> P-2 another possible way for the reaction. P-3 (HCNCH3+ + H), P-5 (cNCHCH(2)(+) + H-2), and P-6 (NCCH3+ + H-2) are exothermic products, but they have higher barriers (more than 40.0 kcal/mol); P-4 (H + HCN + CH3+) and P-7 (H + H-2 + HCCNH+) are endothermic products. They should be discovered under different experimental or interstellar conditions. The present study may be helpful for investigating the analogous ion-molecule reaction in Titan's atmosphere.