A manufacturing method of a flexible display device and a flexible display device are provided. The manufacturing method of the flexible display device includes: forming a conductive heating layer with a first microstructure pattern on a hard substrate; forming a flexible substrate layer on the conductive heating layer, and forming a display device on the flexible substrate layer; performing a heating treatment on the conductive heating layer to separate the flexible substrate layer from the conductive heating layer, and a side of the flexible substrate layer away from the display device having a second microstructure pattern after being separated.