The present disclosure provides a flexible display substrate, a method for manufacturing the same, and a flexible display device, and belongs to the technical field of display. Among them, the method for manufacturing a flexible display substrate includes: providing a carrier substrate; forming a flexible display substrate including a plurality of pre-cuts on the carrier substrate, with the plurality of pre-cuts exposing the carrier substrate; forming an inverted frustum structure on the carrier substrate at the plurality of pre-cuts, an orthogonal projection of a lower end surface of the inverted frustum structure on the carrier substrate is located within an orthogonal projection of an upper end surface of the inverted frustum structure on the carrier substrate; packaging the flexible display substrate; and peeling the flexible display substrate packaged from the carrier substrate.