The invention discloses a preparation method of a magnetic composite nickel oxide catalyst. The method sequentially comprises the following steps that under the constant-temperature water bath condition, hydrogen peroxide and a NaOH dilute solution are dropwise added in a FeCl2 solution, stirring is conducted, the mixture is shifted to an autoclave, reacting is conducted continuously, natural cooling is conducted to room temperature, solid sediment is obtained and added to a sodium dodecyl benzene sulfonate solution, and magnetic organic hydrotalcite is obtained; (3-aminopropyl)triethoxysilane, salicylaldehyde and nickel chloride hexahydrate are prepared into a solution according to the molar ratio of 1:1:1, magnetic organic hydrotalcite is added, and nickeliferous organic complex pillared hydrotalcite is formed; nickeliferous organic complex pillared hydrotalcite is put in a muffle furnace and calcined for 6 h to 8 h at 400 DEG C to 550 DEG C, elements such as carbon and nitrogen are converted into gas to overflow, a channel is formed, and the magnetic synergetic nickel oxide catalyst is obtained. The catalyst is beneficial for adsorption and catalysis of pollutants, and meanwhile the catalyst is beneficial for separation.