Series DMTFD Centre-Insertion Transit Time Ultrasonic Flow Meter is an improved mode for Standard Insertion Series. The Centre-Insertion transducer is easy to mount; two transducers are installed at the same side. One transducer is the same with standard insertion transducer, but the other transducer is always inserted into the centre point of pipe line, the insertion length varies with the pipe line diameter. In fact, the ultrasonic flight distance is half of the standard insertion mode. The difference in time of flight also is half of the standard insertion mode. One obvious advantage of Centre-Insertion Series compared with standard Insertion Series is easy to install. The two transducers are mounted in the same side of pipe line, so even the pipe partially buried underground, it still can be installed in the Centre-Insertion mode. Compared with standard Insertion Series，Centre-Insertion Series is less installation spacing requirement. Its longitudinal space is half of standard insertion series, and almost no transverse space demand.