Flow is one of the important parameters of calibration instrument of blood purification device, but the measuring range of existing liquid flow standard devices can not meet the traceability needs of flow in calibration instrument of blood purification device. In order to solve this problem, a small flow standard device suitable for calibration instrument of blood purification device is developed. The piston metering system, combining grating servo feedback and automatic control technology were adopted to realize automatic measurement of small liquid flow. According to the experiment, the measuring range of this device is (10~2 000) mL/min, the maximum permissible error is ±034%, and the repeatability is better than 006%. Therefore, the device fully satisfies the flow traceability requirement of calibration instrument of blood purification device.