An　optimization　method　combining　Geant4　code　with　genetic　algorithm　was　established　and　applied　to　designs　of　two　types　of　gas　Cherenkov　detectors　(GCDs)　because　of　deficiencies　of　the　traditional　optical　ray-tracing　method.　Improved　efficiencies　and　time　responses　were　obtained　compared　with　results　of　traditional　optical　ray-tracing　method.　The　efficiency　of　GCD　system　through　optimization　is　enhanced　by　20%　while　time　response　is　eliminated　by　7.2%.　The　efficiency　of　GRH　(gamma　reaction　history)　system　through　optimization　is　enhanced　by　91.2%.　Aiming　at　fusion　diagnostic　process,　the　MRNSD　(modified　residual　norm　steepest　descent)　method　was　ascertained　as　signal　recovery　method　for　fusion　reaction　history　diagnosis　through　comparison　study.　The　MRNSD　method　can　recover　sub-nanosecond　signal　distorted　by　response　function　of　which　the　FWHM　(full-width　at　half　maximum)　is　10　times　of　the　signal　to　be　recovered　and　with　10%　Gaussian　white　noise　added,　which　is　suitable　for　fusion　reaction　history　diagnosis.　©　2017,　Editorial　Board　of　Atomic　Energy　Science　and　Technology.　All　right　reserved.