  Southern Spectroscopic Survey Telescope (SSST) is a wide-field spectroscopic
survey telescope that China plans to build in Chile in the next few years. As
an instrument for astronomical spectroscopic survey, the multi-object and
fiber-fed spectrograph (MOFFS) is one of the most important scientific
instruments for SSST. In this paper, we present a recommended optical design
for the MOFFS system based on the Volume Phase Holographic Gratings (VPHG). The
whole design philosophy and procedure, including the analytic method to
determine the initial structure, optimization procedures of the VPHG and the
camera groups, are demonstrated in detail. The numerical results of the final
obtained spectrograph show a superior imaging quality and a relatively high
transmittance for the whole working waveband and the field of view. The design
method proposed in this paper can provide a reference for the design of MOFFS
accommodated in spectroscopic survey telescopes.
