Abstract: To develop the evaluation methods for some nuclides whose measured data are scant, the systematics formulae of thermal neutron fission cross sections were established based on the fission theory. On the basis of the recommended thermal neutron fission cross sections and the height of the fission barrier, the correlations between thermal neutron fission cross sections and excitation energy of saddle point were studied. The parameters of every nuclide with different Z were obtained by fitting. Then, the systematic behaviors of these parameters with Z were studied, and the parity relations were found. The overall systematic formulae of thermal neutron fission cross sections were established by fitting. The results indicate that there are correlations between thermal neutron fission cross sections and Z.