The invention provides a built-in automatic thread trimming mechanism of a
sewing machine. The built-in automatic thread trimming mechanism comprises a driving source and a
sewing machine main shell. A sunken portion is arranged on the rear wall of the
sewing machine main shell, and the driving source is arranged in the sunken portion; a telescopic shaft of the driving source is movably connected with a first lever, one end of the first lever is hinged to the sewing
machine main shell, and the other end of the first lever is hinged to one end of a second connecting rod; the other end of the second connecting rod is hinged to one end of a second lever, and the other end of the second lever is perpendicularly fixed to a cutter shaft; the cutter shaft is rotatably supported in a cutter head, and the cutter head is fixed to the side, which is adjacent to a needle, of the sewing
machine main shell; a movable cutter which is perpendicular to the cutter shaft is fixed to an end of the cutter shaft, is close to the front side wall of the sewing
machine main shell and is opposite to a fixed cutter of the cutter head; a rear housing is fixed to the outer side of the sunken portion on the rear wall of the sewing machine main shell. The built-in automatic thread trimming mechanism has the advantages that various actuators of the built-in automatic thread trimming mechanism are mainly hinged to one another, accordingly, stable transmission effects can be realized, the built-in automatic thread trimming mechanism is low in
noise, the driving source is short in
stroke and small in size, the thread trimming mechanism can be arranged in the sewing machine main shell, and the integral sewing machine is attractive.