The invention provides a method for preparing pentaerythritol and coproducing strontium formate and sodium sulfide, which comprises the following steps of: distilling waste liquor generated in the process of producing pentaerythritol through condensation of formaldehyde and aldehyde under reduced pressure to obtain saturated solution of pentaerythritol, cooling, and filtering and separating to obtain pentaerythritol crystals and filtrate A; washing, drying and crushing the pentaerythritol crystals to obtain a pentaerythritol product; distilling the filtrate A under reduced pressure to obtain saturated solution of sodium formate, cooling, and filtering and separating to obtain sodium formate crystals; dissolving the sodium formate crystals in water, reacting with solution of strontium sulfide, and filtering to obtain clear filtrate C; and distilling the filtrate C, cooling, crystallizing and separating out to obtain a strontium formate and sodium sulfide mixed product.