The invention discloses an automobile seat backrest with a middle armrest. The left end and the right end of an armrest cup holder are hinged to a cup holder rotating shaft. The left end of the cup holder rotating shaft is fixedly supported by an armrest cup holder limiting support. The armrest cup holder limiting support limits the armrest cup holder and is fixed to a large armrest cup holder bracket in a welded mode. The large armrest cup holder bracket is longitudinally welded into a backrest framework. The right side of the cup holder rotating shaft is also provided with an armrest cup holder limiting support and a large armrest cup holder bracket, and the armrest cup holder limiting support and the large armrest cup holder bracket on the right side of the cup holder rotating shaft are in symmetry with the armrest cup holder limiting support and the large armrest cup holder bracket on the left side. A shape supporting steel wire is arranged in back foam in an integrally foam forming mode. The position, close to an armrest cavity, of the steel wire is bent into a U shape along the upper edge, the lower edge and one side edge of the armrest cavity, and the steel wire is embedded into the back foam. The situation that the automobile seat backrest tilts as a result of imbalance between left stress and right stress will not happen, and the problem that soft foam at the edge of the armrest cup holder collapses after being coated with a shell fabric is solved.