Abstract: To improve the verification efficiency of DN15～DN25 water meters, considering the piston water meter verification device has good flow stability, precise adjustment, and high accuracy. due to the difficulty of processing and manufacturing and the high economic cost, its effective volume is small, and it is only suitable for the test of small and medium flow. As a water meter verification device of standard meter, the electromagnetic flowmeter has good stability and high accuracy in large flow, but it is not suitable for detecting medium and small flow. A set of improved verification device of the piston water meter with 0.2 level flow range of (0.01～10) m³/h and electromagnetic flowmeter as standard meter is designed. Through three DN15 rotor wet cold water meters, the flow point errors of Q3, Q2, and Q1 are tested by this device and the static mass method device respectively. The results show that the maximum difference of Q3 point is 0.15%, and the difference of all flow points is less than MPE/5. The test accuracy of the device is verified and showed that the efficiency is improved by 8 times, which meets the verification requirements of DN15～DN25 civil water meters. The piston can regularly check the standard meter online to ensure its measurement accuracy, providing a practical solution to the current widespread problem of inefficient water meter verification.