The invention discloses a system and a method for preparing cement co-production sulfur by utilizing urban wastes and industrial solid wastes. The system comprises a homogenizing tank, a filter press, a drier, a raw material mill unit, a rotary kiln, a cement mill, a hot water storage tank, a dust remover and a reduction fixed bed; red mud, wet sludge and industrial water enter the homogenizing tank to be homogenized and dealkalized, and then enter the filter press to be filter-pressed; a filter-pressed solid material enters the drier to be dried, the dried solid material together with desulfurization gypsum enters the raw material mill unit for raw powder ratio milling; a milled material enters the rotary kiln for high-temperature calcination to obtain a sulphoaluminate clinker; the sulphoaluminate clinker together with desulfurization gypsum enters the cement mill for mixed milling to obtain sulphoaluminate cement; hot water in the hot water storage tank provides heat for the homogenizing tank; sulfur dioxide-containing flue gas generated in the rotary kiln is subjected to dust removal through the dust remover and is conveyed to the reduction fixed bed for reduction to obtain the sulfur.