The coarse space-energy mesh rebalancing method is studied for the purpose of convergence acceleration on two-dimensional multigroup neutron diffusion calculations with a seven-point finite difference scheme, a uniform triangular mesh, and an arbitrary scattering matrix. The rebalancing method provides convergences without numerical instability for a range of fast reactor problems with varying numbers of neutron energy groups and mesh points. The number of outer iterations is decreased with the rebalancing method by a factor of 2 in comparison to the case when only asymptotic fission source extrapolation and successive overrelaxation acceleration techniques are applied. With the rebalancing method, the HIVER code solves the problems 5 to 20 times faster than the existing reference CITA TION code. The relative calculation speed of the reference code increases with the problem size.