Non full pipe flowmeter is an automatic flow measurement instrument that uses the velocity area method to continuously measure fluid flow in open pipelines, such as semi pipe sewage pipelines and high flow pipelines without overflow weirs. It can measure and display data such as instantaneous flow rate, flow velocity, and cumulative flow rate. Especially suitable for the needs of municipal rainwater, wastewater, sewage discharge, and irrigation water pipelines and other metering places. A non full pipe flow meter is composed of an electromagnetic flow velocity sensor, an ultrasonic water level sensor, and a flow display instrument, which continuously measures the flow velocity and liquid level of the fluid in the pipeline. Users only need to input the inner diameter of the circular pipeline or the width of the square pipeline, and it will automatically calculate the flow rate in the pipeline and display the measurement parameters such as instantaneous flow rate, flow velocity, and cumulative flow rate in the pipeline.