The invention discloses a high-precision real-time amplitude measurement device based on self-mixing interference. The device comprises a laser light source, a beam splitter, a photoelectric detector,a reflector, a signal processing unit, a data processing display unit and a measurement subject, wherein the laser light source, the beam splitter, the photoelectric detector, the measurement subjectand the reflector are sequentially connected via an optical path; and the input end of the signal processing unit is connected with the photoelectric detector, and the output end of the same is connected with the data processing unit. The invention also discloses a high-precision real-time amplitude measurement method based on self-mixing interference. According to the device and method providedby the invention, a reference arm of a traditional laser interferometer is not needed, a single-arm optical path is easy to collimate, and the noise sensitivity of the system to the outside is reduced. A self-mixing interference principle is used, so that no specific requirement on coherence of the laser light source is needed, and the freedom of choice of the laser is large. Meanwhile, a gain parameter of the device is controllable, and a measurable minimum amplitude value can reach nanoscale; a signal spectrum feature value is acquired in a frequency domain, stripes do not need to be counted, and real-time wide-range measurement is easy to implement.