Tertiary telescopic column with secondary support function

The invention discloses a tertiary telescopic column with a secondary support function, mainly comprising an outer cylinder, a primary internal cylinder, a secondary internal cylinder and a movable column, wherein the primary internal cylinder and the secondary internal cylinder have great support and telescopic force, the movable column has small telescopic and support force, the bottom of the primary internal cylinder is provided with a bottom valve to control primary internal cylinder lower-cavity liquid to enter and exit so as to ensure that the primary internal cylinder and the secondaryinternal cylinder have the same telescopic and support force, no hole is formed in the bottom of the secondary internal cylinder, the movable column is provided with a slender hole used for secondaryinternal cylinder lower-cavity liquid entering and exiting, a liquid inlet is formed in the head of the movable column, the telescopic and support force of the primary internal cylinder and the secondary internal cylinder of t