The invention discloses a hole type viscous damper with the hole length capable of being automatically adjusted. The hole type viscous damper comprises a cylinder barrel. A piston rod is arranged in the cylinder barrel. The middle of the piston rod is sleeved with a piston. The positions, close to the two ends, of the piston rod are each sleeved with a guide sleeve. The guide sleeves include the left guide sleeve and the right guide sleeve respectively. The right guide sleeve is located at the right end of the cylinder barrel. A right attached lug is arranged at the outer end of the right guide sleeve and connected with the right end of the piston rod. The left end of the cylinder barrel is sealed through an end cover. The outer side of the end cover is connected with a left attached lug. When the piston rod reciprocates, energy consumption liquid in a left cavity and a right cavity of the piston and energy consumption liquid in a damping hole flow at a high speed, and when the running speed is high, the damping force can be large, the distance between sliding blocks on the two sides becomes small through pressure in the liquid, the length of the damping hole can become small, accordingly the increasing amplitude of the damping force can become small, and therefore the hysteresis curve of the damper can be fuller or the energy consumption efficiency is higher.