A method for preparing an aripiprazole type I microcrystal, including the following steps: dissolving aripiprazole in an acidifier, acquiring a medicament-having acid solution; adding an alkalizer while stirring, then adding water or aqueous ethanol 10 to 60 wt % while stirring, and separating by precipitation the aripiprazole type I microcrystal. Furthermore, a method for preparing a solid preparation having the aripiprazole type I microcrystal, an aripiprazole microcrystal having an average particle size of less than 20 μm, and a solid preparation having the microcrystal. The method for preparing the aripiprazole type I microcrystal allows reduced pollution and loss, great safety, easy and convenient, reduced use of organic solvents, obviated need for demanding process conditions (such as cooling condition) and apparatus, low cost, and facilitated applicability in industrialized manufacturing. This solid preparation provides great stability, solubility, and bioavailability, reduced individual differences, and reduced content of related substances.