The invention discloses a device for detecting the deformation of a transformer winding based on pulse on-line injection, and belongs to the technical field of on-line detection of power equipment. The device comprises an all-solid-state high-voltage nanosecond square-wave pulse generator, a signal injection and protection circuit unit, a transformer signal sensor unit, a current sensor unit, a high-pass filter unit, a signal collection unit, and a signal processing unit. The device achieves the non-intrusive on-line detection of the transformer winding. During detection, a conventional wiring mode of a power system does not need to be changed, so the system is safer. The system employs a high-voltage nanosecond pulse signal excitation winding, avoids power frequency and a part of interference signals, improves the capability of anti-electromagnetic interference, can achieve quick detection under the condition that only several pulses are inputted because a high-voltage nanosecond pulse signal contains abundant frequency spectrum components, improves the speed and efficiency of detection, greatly reduces the size and number of an acquired device, and reduces the cost of manufacture.