In order to meet the current demand for liquid flow velocity measurement in miniaturized equipment, a new method suitable for measuring fluid velocity in non-full tube is proposed by combining spatial filtering velocity measurement with capacitively coupled contactless conductivity detection ( C 4D) technology. A C 4D sensor with an axial two-electrode structure is designed. The threedimensional simulation model of the sensor is established using COMSOL simulation software, and the spatial sensitivity distribution characteristics of the sensor is analyzed. The principle of liquid velocity measurement is theoretically deduced based on the spatial filtering effect of the sensor, and the mathematical expression of velocity measurement is obtained using the method of equivalent peak frequency. On this basis, a set of C 4D liquid flow velocity measurement system that is suitable for spatial filtering was designed, and the good spatial filtering effect of C 4D sensor was verified with this measurement system. The experiment results show that the measurement method has good feasibility. In the velocity range of 1. 39~ 2. 35 m/ s, the absolute error of measured velocity is within 5% .