The invention provides a method for preparing pentaerythritol as well as formic acid and sodium nitrate. The method comprises the following steps: waste liquor generated during the production of pentaerythritol through condensation of formaldehyde and acetaldehyde is distilled under reduced pressure to obtain a saturated pentaerythritol solution, the saturated pentaerythritol solution is then cooled, and pentaerythritol crystals and a filtrate I are obtained through filtering separation; the pentaerythritol crystals are washed, dried and crushed into pentaerythritol products; the filtrate I is distilled under reduced pressure into a saturated sodium formate solution, the saturated sodium formate solution is cooled, and sodium formate crystals are obtained through filtering separation; the sodium formate crystals are dissolved in water and then react with a nitric acid solution to obtain a solution, and then the solution is filtered to obtain a clear filtrate III; the filtrate III is distilled under reduced pressure to obtain a saturated sodium nitrate solution, and the saturated sodium nitrate solution is cooled, crystallized and filtered to obtain sodium nitrate crystals and a formic acid solution; the sodium nitrate crystals are washed, dried and crushed to obtain sodium nitrate products; and the formic acid solution is concentrated to obtain formic acid products.