In this study, biological ash samples were prepared by establishing a high-capacity microwave integrated device for carbonizing and ashing. Radioactive nuclides in biologically derived ash samples using high-purity germanium gamma spectrometry were directly measured for rapid determination of γ radionuclide activity concentration in environmental bio-samples from nuclear power plant surroundings. A comparison with the traditional ash preparation method was also conducted. The results showed that the microwave-ash preparation method can improve the preparation efficiency of biological samples by approximately 2 to 5 times, with a relative deviation of less than 14.8% for parallel samples and a spike recovery rate ranging from 87.0% to 116%. A paired T-test revealsed no significant difference between the two methods. The proposed method has the advantages of high accuracy, high analytical efficiency, simple operation, greater security, and environmental friendliness. It is an ideal method for quickly determining γ radionuclide activity concentration in biological samples.