A method of preparing a catalyst, comprising: (1) mixing a ZSM-5 molecular sieve, a phosphorus source, a matrix material, a bonding agent and water to formulate an aqueous slurry, wherein the total content of the components except for water is 20-50 wt % based on the total weight of the aqueous slurry; (2) spray drying the slurry obtained in step (1) to obtain a granular intermediate product; and (3) calcining the granular intermediate product obtained in step (2) to obtain the catalyst used for preparing olefin from methanol in a fluid bed. The invention also provides a catalyst prepared according to said method, and a process of preparing olefin from methanol using said catalyst. In the methanol-to-olefin process, the conversion of methanol is >99%; the propylene selectivity is high; and the C4 selectivity is up to 32%.