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For understanding the physics of energetic particles, the deuterium experimental campaignsstarted in Large Helical Device (LHD) from March 2017. To investigate the behavior ofenergetic particles, a Fast-ion D Alpha (FIDA) diagnostic was installed on the LHD. In theFIDA diagnostic, the Doppler-shifted D alpha light from fast-neutrals are utilized as signals ofenergetic particles, where these fast-neutrals are produced by the charge exchange processbetween fast-ions in the plasma and actively injected neutrals by neutral beam (NB). Theadvantages of the FIDA diagnostic are the velocity and the spatially resolved measurement offast-ions at the crossing point between its line of sight (LOS) and the incident line of NB. Themost recent FIDASIM is enhanced to simulate signals produced in three-dimensional magneticconfigurations. The new version of FIDASIM uses the fast-ion distribution function producedby GNET as input to simulate FIDA signals at LHD. In order to validate the new version of thecode, measurements of radial profiles of fast-ions using the FIDA diagnostic are performed inmagnetohydrodynamic (MHD)-quiescent plasmas. The measured spectra are in good agreementwith the theoretical prediction by 3D-supporting FIDASIM at the center of the plasma(R = 3.5 m~3.7 m, reff/a99 = −0.28~0.05) on the LHD when the line averaged electron densityis ne_avg < 1.23 × 1019 m−3. On the other hand, the measured spectra are in disagreement withthe theoretical prediction by 3D-supporting FIDASIM at even the center of the plasma when theline averaged electron density is ne_avg ≥ 1.23 × 1019 m−3.