  Focused on the generation and evolution of vast complementary pairs of the
primary fission fragments at scission moment, Dinuclear and Statistical Model
(DSM) is proposed. (1) It is assumed that the fissile nucleus elongates along a
symmetric coaxis until it breaks into two primary fission fragments. (2) Every
complementary pair of the primary fission fragments is approximatively
described as two ellipsoids with large deformation at scission moment. (3) The
kinetic energy in every complementary pair of the primary fragments is mainly
provided by Coulomb repulsion, which is explicitly expressed through strict
six-dimensional integrals. (4) Only three phenomenological coefficients are
obtained to globally describe the quadrupole deformation parameters of
arbitrary primary fragments both for $^{235}$U($n_{th}, f$) and
$^{239}$Pu($n_{th}, f$) reactions, on the basis of the common characteristics
of the measured data, such as mass and charge distributions, kinetic energy
distributions. In the framework of DSM, the explicit average total kinetic
energy distribution $\overline{TKE}(A)$ and the average kinetic energy
distribution $\overline{KE}(A)$ are consistently represented. The theoretical
results in this paper agree well with the experimental data. Furthermore, this
model is expected as the reliable approach to generally evaluate the
corresponding observebles for thermal neutron-induced fission of actinides.
