Sofa with turnable backrest

A sofa with a turnable backrest, comprising a sofa seat frame, a backrest body, and an extension mechanism, wherein the backrest body is connected to the sofa seat frame through the extension mechanism, and the extension mechanism is configured to turn and flatten the backrest body from a backrest position of the sofa seat frame to a position above a sitting position, and configured to turn the backrest body back to the backrest position;

• the extension mechanism comprises a skeleton, a first connecting rod, a first extension rod, a second connecting rod, a second extension rod, and a turnable base connected to the backrest body, two ends of the first connecting rod form a revolve pair with a first end of the first extension rod and the skeleton, respectively, the second connecting rod is configured to be staggered with the first extension rod and forms a revolve pair at an intersection point, two ends of the second connecting rod form a revolve pair with a first end of the second extension rod and the skeleton, respectively, a second end of the first extension rod and a second end of the second extension rod form a revolve pair with the turnable base, respectively, and the skeleton is fixed to the sofa seat frame.