Abstract: A method of spontaneous deposition of ²¹⁰Po on a silver disc was used to prepare the standard plane source in a ²¹⁰Pb solution. The prepared source was measured by an alpha spectrometer. There was a unique alpha peak of 5.304 MeV with a full width at half maximum of 23.92 keV in the measured spectrum. A plateau length of about 1000 V was given in the plateau curve measued with a multi-wire proportional counter. The determined surface emission rate was 2.565 ×10⁴ min^-1 at JAN. 3RD, 2019, with the extended uncertainty of 2.7% (k=2). Some MPC9604 gas-flow low background gross alpha and gross beta counters were used to test the source according to the verification regulation JJG 1100-2014. All the α detection efficiencies were not less than 77%, the repeatability within 1.5% and the α interference to β channel not greater than 2.5%. It’s showed that the prepared source was in good quality and performance to meet the calibration of gas-flow low background gross alpha and gross beta counters.