The misfit and coherent elastic energy caused by omega particles in beta matrix is quantitatively calculated in this study. First, the coherent strain matrixes for four omega variants are established including the misfit parameters based on Khachaturyan's theory. Then, the misfit and coherent elastic energy in athermal beta -> omega transition, and isothermal beta -> omega transition are calculated, respectively. The calculation results indicate that the coherent elastic energy gets maximum value when chi(Nb) = 0.08 (Nb content) and gets minimum value when chi(Nb) = 0.1518 in quenching Zr-Nb alloys, which are in fair agreement with experimental results. For isothermal beta -> omega transition, the misfit and coherent elastic energy depend on composition and aging temperature. The misfit caused by isothermal omega phase is much larger than the one caused by athermal omega phase. This results in larger coherent elastic energy in isothermal beta -> omega transition. In addition, the misfit is found as an approximate linear function of temperature and composition for Zr-Nb alloys, and the coherent elastic energy is revealed as an increasing function of vertical bar nu(F)-nu(S)vertical bar for the two kinds of transition.