Abstract: A variational formula combining mixed finite element method with discontinuous finite element method is derived for solving the two group neutron diffusion equation in 2D. According to the variational formula, a numerical test is given whose result proves that the variational formula is reasonable and practicable. In order to improve the precision of the calculation, there are more to be studied.

Key words: neutron transport equation, neutron diffusion equation, mixed and discontinuous finite element, Ravairt-Thomas element