The most direct method of studying Peyrard-Bishop-Dauxois (PBD) model is the molecular dynamics simulation method. The phase transition of (PolyA/PolyT)(100) duplex into the denaturated state is studied in the PBD model by the method of collisional molecular-dynamical modeling. The temperature dependencies of the total energy and heat capacity of the duplex are calculated. Unlike other calculations, we have obtained a wide peak of heat capacity in the region of temperature transition. The approach applied can be used to calculate the statistical properties of the duplexes of any length and nucleotide composition as well as proteins and other macro-molecules.