The invention provides single anion pillared layered double hydroxides and a preparation method thereof. At room temperature, (MII)(NO3)2 question mark 6H2O and M(III)(NO3)2 question mark 9H2O are respectively weighed and prepared into nitrate aqueous solution according to the mol ration of 2-4 of (MII)/M (III); in addition, NaOH and Na2CO3 are respectively weighed and prepared into lye; under thestrong magnetic stirring, the lye and the nitrate aqueous solution are simultaneously and dropwise added into a container at uniform speed and dripped until pH is 10.0 plus or minus 0.5; the blendedserum is aged for 8h at the temperature of 65 DEG C, filtered and repeatedly washed till being neutral, and dried for 24h in a vacuum drying cabinet at 700 DEG C; the dried matter is baked for 2h at the temperature of 450 DEG C to form layered double oxide; under protection of N 2, after the baked layered double oxide is placed in to a container which has single anion solution, put in a constant temperature oscillator with 180r/min for shaking 24h, filtered, and then washed two or three times, and the product is prepared. The invention uses 'memory effect' of hydroxides, and the layered structure reconstruction of LDHs to lead that the anion enters into interlamination, thus forming the new structure LDHs.