From mass conservation and energy conservation of hotspot, dynamics of hotspot combustion involving shell-mix are constructed by recalculating special internal energy and heat capacity, in which bremsstrahlung radiation loss and other energy transfer are considered. With power balance in hotspot, relations between fractions of shell-mixing in hotspot and ignition threshold and self-sustainable combustion are investigated. Theoretical analysis and numerical simulation show that enhancement of radiation loss induced by shell-mixing plays dominated role in failure of ignition. By adjusting materials and mixing fraction, effects to combustion paths are studied. Finally, two methods for degrading impact of shell-mixing are proposed.