The invention discloses a cable fixing device applied to a mechanical arm of a robot. An annular boss is formed in the center of a base plate of the cable fixing device. An annular shaft body is formed on the upper end face of the annular boss. An annular groove is formed in the upper end face of the portion, on the periphery of the shaft body, of the annular boss. A torsional spring is inserted into the groove. One end of the torsional spring is fixedly inserted to the annular boss, and the other end of the torsional spring is fixedly inserted into an H-shaped rotary disc. The rotary disc is composed of an annular winding column in the middle and disc bodies at the two ends. The shaft body is sleeved with the rotary disc in an inserting manner. A shaft sleeve is formed on the bottom face of the rotary disc. The annular boss is sleeved with the shaft sleeve in an inserting manner. An annular limiting groove is formed in the outer wall of the annular boss. T-shaped limiting columns are inserted into the limiting groove. The limiting columns are fixedly inserted into the shaft sleeve. According to the cable fixing device applied to the mechanical arm of the robot, the cable fixing device is fixed to the mechanical arm, and meanwhile a cable is wound around the fixing device; and when the mechanical arm operates, the cable is wound out of the fixing device, the length of the cable is increased, and operation of the mechanical arm is not influenced.