Temperature-constant and pressure-constant molecular dynamics simulations of crystalline 1,4-linked poly(cyclohexa-1,3-diene) (CHD) were performed using the COMPASS force field. Powder X-ray diffraction spectra calculated from the simulated atomic coordinates were compared with the measured spectrum of the crystal of 1,4-linked poly(CHD), obtained using a bis(allylnickel bromide) (ANiBr)/methylaluminoxane (MAO) catalyst. As a result of the comparison, the geometrical isomerism of the 1,4-linked poly(CHD) obtained with the ANiBr/MAO catalyst was found to be cis syndiotactic.