The present invention belongs to the technical field of radioactive substance detection, and relates to a radioactive aerosol filter membrane standard [Gamma] source radioactive activity fixed value method. The method comprises the following steps in order: (1) dripping of sources: dripping radioactive solution with known radioactive activity onto a filter membrane for filtering; (2) compression moulding: putting the filter membrane after filtering onto a bottom lining filter membrane to fold the filter membrane and perform compression moulding of the filter membrane, and folding the bottom lining filter membrane which is used to put the filter membrane after filtering to the same shape as the filter membrane to perform compression moulding according to the same method; and (3) fixing of avalue: multiplying the total activity of radioactive solution through dripping source by a ratio of a counting rate of the filter membrane through compression moulding to the sum of a counting rate of the filter membrane through compression moulding and a counting rate of the bottom lining filter membrane through compression moulding to obtain the radioactive activity fixed value of the radioactive aerosol filter membrane standard [Gamma] source. The method is employed to allow the fixed value of the radioactive activity in a radioactive aerosol film standard [Gamma] source sample to be moreaccurate.