A keycap forming method includes the following steps. Firstly, a stabilizer bar is formed through a first male mold and a first female mold according to an injection molding process, and a keycap is formed through a second male mold and a second female mold according to the injection molding process. Then, the stabilizer bar is fixed on the first male mold, and the keycap is fixed on the second female mold. Then, the first male mold and the second female mold are stacked on each other, so that the stabilizer bar and the keycap are combined together. Then, the first male mold and the second female mold are separated from each other, so that the stabilizer bar is detached from the first male mold. By using the keycap forming method, it is not necessary to manually assemble the stabilizer bar with the keycap.