A flexible touch display panel and a method and a system for detecting a folding angle of the flexible touch display panel are provided. The method includes inputting a first scan signal to the touch electrode and obtaining a channel capacitance value of the touch electrode, determining whether the channel capacitance value is greater than a sleep threshold, controlling the flexible touch display panel to enter a sleep state in a case that the channel capacitance value is greater than the sleep threshold, and determining a capacitance value interval in which the channel capacitance value is located and determining a current folding angle of the flexible touch display panel based on a correspondence between the capacitance value interval and the folding angle in a case that the channel capacitance value is not greater than the sleep threshold.