The invention discloses a Coriolis mass flowmeter amplitude self-adaptation control method based on fluid state detecting. An ultrasonic transducer is arranged at an inlet end of a Coriolis mass flowmeter detecting pipe, through the attenuation effect on ultrasonic signals from impurities such as air bubbles, whether the amplitude value of received signals is changed suddenly is detected and judged via a threshold value comparer, whether impurities exist at a fluid state is obtained, and then switching of fixed PID and fuzzy PID amplitude controllers is carried out. According to the method, by detecting on the fluid state and self-adaptation controller switching, high-precision stable state control performance can be kept, system dynamic response speed can be improved, measuring pipe vibration stopping is avoided, stable vibration is reestablished quickly, the self adaptability of Coriolis mass flowmeter measuring pipe amplitude control is enhanced, and the reliability and the metering performance of a Coriolis mass flowmeter under a complex working condition are improved.