A guide device for an elevator slide door includes a guide block (2), arranged on a lower edge of a slide door (1) for opening/closing a gateway of the elevator; and a guide slot (5), arranged on a doorsill (4) of the gateway and the guide block (2) may jogging slidably. The guide slot (5) has a broad width part (6) and a narrow width part (7) locating on the superior side of the broad width part(6). In a plane being vertical with the length direction of the guide slot (5), the transversal width of the narrow width part (7) is less that that of the broad width part (6). The guide block (2) has an anti-falling part (8) and is jogged with the broad width part (6), and the transversal width of the anti-falling part (8) is larger than that of the narrow width part (7).