The invention discloses a molecular sieve based catalyst for directly preparing polymethyl benzene and preparation and usage methods thereof. The molecular sieve based catalyst for preparing the polymethyl benzene (tetramethylbenzene- hexamethylbenzene) by using CO, methanol, dimethyl ether or C1-C8 aromatic hydrocarbons and other raw materials uses a ZSM-12 molecular sieve as a main component, can form a multi-component catalyst with a metal and/or structural strengthening agent and/or a stability additive. According to a preparation method of the ZSM-12 molecular sieve and a method for preparing the multi-component catalyst by utilizing the ZSM-12 molecular sieve, the temperature is 450-520 DEG C and the weight space velocity of raw materials is 0.2-15 g/g/h in aromatization reaction, and the polymethyl benzene yield in an obtained organic liquid product is above 80%.