The digital rotary viscometer, controlled by a single-chip computer, is an intelligent instrument with data acquisition, processing, and Chinese character display. The digital rotary viscometer controls the stepper motor to operate accurately and smoothly according to the set rotation speed, and rotates the rotor through the traveling ribbon. When the rotor is not subjected to resistance, the rotor and the motor rotate synchronously; when the rotor is subjected to measured fluid resistance, the rotation of the rotor of the digital rotational viscometer will lag behind the motor. When the tension of the balance spring and the resistance of the liquid reach equilibrium, the lag of the rotor lagging behind the motor is fixed. By measuring the opening angle, according to the set speed and rotor, the digital rotary viscometer calculates the viscosity of the measured liquid and displays it on the LCD screen.