The present invention relates to a flexible display substrate and a flexible display device for solving the problem that the bending of a traditional flexible display substrate may makes the regions differ in brightness. The flexible display substrate includes a flexible substrate, a plurality of TFT structures and a plurality of OLED devices disposed on the flexible substrate, and a variable resistor disposed between the at least one OLED device and the corresponding TFT structure and having a strained resistance effect. One end of the variable resistor is electrically connected with the anode of the OLED device, and the other end of the variable resistor is electrically connected with the source electrode or the drain electrode of the TFT structure; the flexible display substrate is bent towards the backlight side, and the resistance value of the variable resistor increases; and when the flexible display substrate is bent towards the light incident side, the resistance value of the variable resistor is reduced. Since the resistance value of the variable resistor can change with the deformation of the flexible display substrate when the flexible display substrate is bent, the brightness of the different regions of the display substrate can be improved by the change of the resistance value.