An arsenic compound solution, and an albumin nanoparticle and a lyophilized preparation prepared using same and entrapping an arsenic compound. The arsenic compound solution is prepared using the following method: adding As2O3 powder in sterile deionized water to obtain a suspension, 6 to 25 mg of As2O3 powder being added in every mL of sterile deionized water; dripping an NaOH solution to the obtained suspension until the powder is fully dissolved and adjusting the pH of the solution to 7.5 to 9, and making the concentration of the obtained arsenic compound solution be 5 to 20 mg/mL in terms of the added As2O3. The albumin nanoparticle is prepared by mixing an albumin solution and the arsenic solution and the arsenic solution with the mass ratio of the added As2O3 in arsenic compound solution to the albumin ranging from 1:5 to 1:20 and using a method of solvent removing and physical curing.