The utility model provides an upper thread grabbing mechanism of a sewing machine, belongs to the machinery technology field, and helps to solve problems that a conventional upper thread clamping device of a sewing machine is instable in work. The upper thread grabbing mechanism of a sewing machine comprises a motor, a connecting rod and a thread grabbing piece. The motor is fixedly connected inside a sewing machine body. One end of the connecting rod is hinged to a side portion of a rotating shaft of the motor, and the other end of the connecting rod is connected with the thread grabbing piece. The mechanism also comprises a sensing sheet, a first sensor, a second sensor and an alarm. The sensing sheet is fixedly connected to the rotating shaft of the motor. The first sensor and the second sensor are fixedly connected inside the motor and are positioned at two sides of the sensing sheet respectively. When the sensing sheet swings to the first sensor, the first sensor emits a signal to make the motor stop working and the above thread grabbing piece stays in a position to be grabbed. When the sensing sheet swings to the second sensor, the second sensor emits a signal to enable the alarm to be switched on. The upper thread grabbing mechanism of a sewing machine has the advantages of simple structure and more operation stability.