In order to explain the large permittivity of liquid cyanogen consisting of centrosymmetric molecules, a molecular dynamics simulation which includes all degrees of freedom of vibration, rotation, and translation has been performed. The intramolecular potential energy is expressed in terms of the internal coordinates with quadratic, cubic, and quartic force constants. The intermolecular potential consists of an atom-atom pair potential with Coulombic and Buckingham terms. The simulation has given an adequate value of self-diffusion coefficient and a typical form of radial distribution function for the liquid state. The simulation has reproduced well the large value of the permittivity observed in experiments, suggesting that the value results from the extraordinarily large atomic polarization brought by the intramolecular bending motion in an antisymmetric mode. The simulation has also suggested that the nitrogen atoms collide with each other more frequently than with carbon atoms and the collision shifts the normal frequencies related to the N=C bond to higher frequency. The infrared and Raman spectra together with the real and imaginary parts of the refractive index have also been calculated.