The invention provides a method for preparing chromium hydroxide, lead chloride and mixed nitrate from chromium slag. Chromium slag is reacted with hydrochloric acid to obtain a mixed chloride of chromium chloride, calcium chloride, magnesium chloride and aluminium chloride. The reactant is treated with extraction filtration to obtain mixed chloride and a filter cake containing silica. The mixed chloride is added with excess industrial water, so that chromium chloride is hydrolyzed to trivalent chromium hydroxide which is precipitated; and extraction filtration is carried out to obtain clear calcium, magnesium and aluminium mixed chloride and a chromium hydroxide filter cake. The chromium hydroxide filter cake is washed, dried and crushed to obtain a chromium hydroxide product. The calcium, magnesium and aluminium mixed chloride is reacted with a lead nitrate solution to generate lead chloride and calcium, magnesium and aluminium mixed nitrate. A calcium, magnesium and aluminium mixed nitrate solution is treated with reduced pressure distillation, cooled and crystallized to obtain a calcium, magnesium and aluminium mixed nitrate product. Lead chloride is washed, dried and crushed to obtain a lead product.