Given the scarce dynamics theoretical information and the experimental controversies about the HCN(v1,v2,v3) vibrational populations, the main aims of the present work are two-fold. Firstly, to develop for the first time an analytical fulldimensional potential energy surface (PES) to describe the nuclei motions, and secondly, based on this PES, to perform an exhaustive dynamics analysis at room temperature, to simulate the experimental evidence, on the HCN(v1,v2,v3) vibrational populations and other dynamics properties not experimentally reported. The present paper is organized as follows. In Section 2, an analytical full-dimensional surface was developed, named PES-2023. It is basically a valence bond functional augmented with molecular mechanic terms, VB-MM, depending on a series of adjustable parameters, which represents in a smooth and continuous way this reactive system with ten bodies and 24 degrees of freedom. The new surface was based on high-level electronic structure calculations to locate and characterize (using the vibrational frequencies) all stationary points and the reaction path: reactants, products, saddle point, with special attention to the intermediate complexes in the entrance and exit channels. This information represents the input data.