The utility model discloses a device for controlling the phthalocyanine blue B acid expansion end point by an acid expansion method. The device comprises a reaction kettle, a stirring shaft, a motor fixing device and a motor, wherein a stirring paddle is arranged under the stirring shaft; the upper end of the stirring shaft is fixed with a rotating shaft of the motor; the motor is arranged on the motor fixing device; the motor is connected with a voltage source; the device is characterized in that an ampere meter is connected between the motor and the voltage source in series. The device is simple in structure; a relationship between the readings of the ampere meter and reaction conditions can be formed, so that the phthalocyanine blue B acid expansion end point control operation is simple and convenient, the product quality is stable, and the problems of pollution to a sampled object and the material loss can be solved in the sampling process.