Abstract: In order to trace strictly the changes of nuclide density with burnup in a fission reactor, the independently developed codes by Chebyshev Rational Approximate Method (CRAM) and widely applied ORIGEN2 were adopted to solve large depletion chains to solve depletion equations based on Burnup Matrix Methods. The values are compared and analyzed with the aspects of computational accuracy, efficiency and step stability. The results show that CRAM can provide similar density solutions of important nuclides with a little slower speed and a much better step stability than those of ORIGEN2.