Filtering efficiency of the Chinese-made filter 1 hasbeen measured by the double-filter method with only one set of measurementequipment. The β counts of the two filters are measured in turn forevery 3 minutes, from which the decay constants are extracted to be0.0131 min-1 and 0.0129 min-1 for the first and second filterrespectively. 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.