The present invention provides a method for preparing a pharmaceutical composition containing a pyrrolo-fused six-membered heterocyclic compound or a pharmaceutically acceptable salt thereof. Specifically, the invention provides a preparation method of a pharmaceutical composition, the method containing: mixing 5-(2-diethylamino-ethyl)-2-(5-fluoro-2-oxo-1,2-dihydro-indol-3-ylidene-methyl)-3-methyl-1,5,6,7-tetrahydro-pyrrolo[3,2-c]pyridin-4-one or a pharmaceutically acceptable salt thereof with at least one filler, and then granulating the mixture. The pharmaceutical composition of the invention features a rapid dissolution and good stability.