Aimed at the long-term stability and reliability problem for ultrasonic water meters, this paper first analyzes the possible reasons caused the problem from measurement principle, and proposes new technology programs from measurement principle, measurability design, and measurement equipment. Firstly, it proposes a measurement principle of ultrasonic flight time based on echo attenuation detection. It avoids the first echo detection error caused by hardware attenuation or noise, which exists in the measurement principle of ultrasonic flight time based on first echo detection. It also proves the feasibility of the echo attenuation detection-based measurement principle. Secondly, it proposes the design method and equipment of ultrasonic liquid flow instrument with improved measurability. Thirdly, it proposes a test system suitable for ultrasonic liquid flow instrument, to resolve the problems in current ultrasonic water meter measurement. By providing systematic technology programs for the long-term stability and reliability problem, this paper lays a good foundation for the commercial application of ultrasonic water meters. The present analysis, principle and method can also be applied to other ultrasonic liquid flow meters such as ultrasonic gas meters and ultrasonic oil meters.