A multi-group pin power reconstruction method that fully exploits nodal information obtained from global coarse mesh solution has been developed.It expands the intra-nodal flux distributions into nonseparable semi-analytic basis functions,and a colorset based form function generating method is proposed,which can accurately model the spectral interaction occurring at assembly interface.To demonstrate its accuracy and applicability to realistic problems, the new method is tested against two benchmark problems,including a mixed-oxide fuel problem.The results show that the new method is comparable in accuracy to fine-mesh methods. A multi-group pin power reconstruction method that fully exploits nodal information obtained from global coarse mesh solution has been developed. It expands the intra-nodal flux distributions into nonseparable semi-analytic basis functions, and a colorset based form function generating method is proposed, which can accurately model the spectral interaction occurring at assembly interface. To demonstrate its accuracy and applicability to realistic problems, the new method is tested against two benchmark problems, including a mixed-oxide fuel problem. The results show that the new method is comparable in accuracy to fine-mesh methods.