The invention discloses a pulse injection time control method for online detection of transformer winding deformation. Exciting pulses are injected into a capacitive coupling ring in the power grid voltage processing peak. The pulses are injected into the capacitive coupling ring in the power grid voltage processing peak so that the problem of misjudgment caused by the nonlinear effect of the iron core on the detection result can be solved. Meanwhile, the invention also discloses a pulse injection time control device for online detection of transformer winding deformation. The pulse injection time control device comprises a control module and a pulse source. The control module generates trigger pulses in the power grid voltage processing peak to trigger the pulse source. The pulse source injects the exciting pulses into the capacitive coupling ring.