The present invention relates to a preparation method for an alumina microsphere. The preparation method is characterized by comprising the following steps: adding an alumina precursor into a gellan gum solution at the temperature of 65-90 DEG C to form an alumina precursor-gellan gum suspension; and adding the suspension into an oil phase at the temperature of 80-100 DEG C and stirring at high speed, adding into a cation solution after cooling and continuing stirring to obtain a gel microsphere; and washing, drying and firing the gel microsphere to obtain the alumina microsphere. The method has the advantages of high forming speed, no pollution during preparation and low production cost; moreover, the method has simple operational steps and facilitates industrial production; wear of the production is low; a particle size can meet requirements of various reactors.