Filtering efficiency of the Chinese-made filter 1 has been measured by the double-filter method with only one set of measurement equipment. The β counts of the two filters are measured in turn for every 3 minutes, from which the decay constants are extracted to be 0.0131 min^-1 and 0.0129 min^-1 for the first and second filter respectively. After correcting the β counts of the second filter, the filtering efficiency of the filter is obtained to be (87.4±0.7)% in average.