The invention discloses pillared hydrotalcite and a preparation method thereof, relates to hydrotalcite and a preparation method thereof, and solves the problems of easy agglomeration and long preparation time of the conventional pillared hydrotalcite. The structural formula of the pillared hydrotalcite is [M2+1-xM3+x(OH)2]x+[An-]x/n.zH2O, wherein M2+ and M3+ are laminar main body ions, An- is an interlayer ion, x is more than or equal to 0.20 and less than or equal to 0.34, and z is the number of crystal water. The method comprises the following steps of: dripping aqueous solution of mixed salt containing M2+ and M3+ and aqueous solution of alkali sodium carbonate into the stirring water, and obtaining a bimetallic composite oxide by microwave crystallization and sintering; and preparing reduction solution from the bimetallic composite oxide, sodium hydroxide and soluble salt of the interlayer ion An-, and performing microwave crystallization and sintering on the reduction solution to obtain the pillared hydrotalcite. The pillared hydrotalcite of the invention is difficult to agglomerate, the exchange time of the interlayer negative ions is only 10 to 20 minutes, and the pillared hydrotalcite can be used in the macromolecular flame-retardant field.