The invention provides a method for preparing pentaerythritol, and co-producing manganese formate and sodium carbonate, which comprises: distilling waste liquid from the production of pentaerythritol by the condensation of formaldehyde and aldehyde under reduced pressure to obtain saturated solution of pentaerythritol, cooling, and separating by filtering to obtain pentaerythritol crystals and filtrate I; washing, drying and crushing the pentaerythritol crystals to obtain a pentaerythritol product; distilling the filtrate I under reduced pressure to obtain saturated solution of sodium formate, cooling, separating by filtering to obtain sodium formate crystals, dissolving the sodium formate crystals in waster, reacting the sodium formate crystals with solution of manganese carbonate, and filtering to obtain clear filtrate III; and distilling the filtrate III under reduced pressure to obtain saturated solution of sodium carbonate, cooling, crystallizing and filtering to obtain sodium carbonate crystals and solution of manganese formate, washing, drying and crushing the sodium carbonate crystals to obtain sodium carbonate products, and concentrating the solution of manganese formate to obtain a manganese formate product.