The present disclosure discloses a detection circuit of a gate driver, an array substrate, a display device and a detection method thereof. Gate scanning signals of each of the signal output ends are derived to a detection signal line through signal deriving circuits, such that the gate scanning signals are transmitted to a discrimination circuit outside the array substrate. The discrimination circuit can acquire in real time and record the gate scanning signals, so as to detect the gate scanning signals in real time, and further rapidly diagnose whether the gate scanning signals are abnormal based on detection results, and rapidly locate the positions at which the gate scanning signals are abnormal, so as to timely troubleshoot the fault.