The invention discloses a method and device for detecting mass flow rate of pulverized coals in a process of conveying the pulverized coals. Sound waves generated by frictions and collision of fluid particles in a non-invasive pick-up pipe with a pipe wall are used to detect medium flow rate in the pipe, thereby solving the problem of large errors in a metering method of the pulverized coals, and improving the measuring accuracy. Sound wave detection is a non-invasive detection method, and a detection device is simple, safe, environmental-friendly, and is suitable for online detection in an industrial production process. A sound wave sensor array is used, and influences of unstable conveyance of the pulverized coals on the measuring accuracy can be effectively eliminated by fusing data of a plurality of sensors. Compared with the prior art, flow velocity, humidity ratio, particle size and mass flow-rate detection technologies based on the sound wave detection are more sensitive, and higher in the detection accuracy, and can be used for replacing a radioactive density meter harmful to a human body.