Abstract: To achieve metrological calibration of nL/min-level liquid ultra-microflow, a piston-type liquid ultra-microflow standard device based on the interference method has been developed. This device employs laser interference measurement technology to ensure precise capture of the syringe piston’s micrometer-level displacement. By establishing a flow calculation model based on the syringe's inner diameter and piston displacement, the uncertainty of each component in the device is analyzed and evaluated. The study used syringes of various specifications to test ultra-microflows in the range of 1–1000 nL/min. Experimental results demonstrate that the device can detect microscopic changes in ultra-microflow, exhibitings excellent flow response capability. Calibration errors for the syringe pump were below 1%, with an expanded uncertainty of less than 4% (k = 2). Finally, comparative experiments between gravimetric and interference method standard devices demonstrated consistent error trends in syringe pump calibration. Further calculation of normalized deviation validated the accuracy of the interference method device and the validity of its uncertainty assessment results.