Abstract: ~(241)Am smoke detector has been widely used to protect the people and their property from fire disaster. The ~(241)Am radioactive source is the core part of the detector. Its α-spectrum is one of the important characteristics to guarantee the quality of the detector. The α-spectra have been examined in this work under different thickness of the gold foil with which the radioactive area is covered.The energy calibration of the spectrometer has been done using the mixture alpha standard source (~(241)Am, ~(239)Pu and ~(244)Cm) made in U. K. The linearity of energy from 2 MeV to 6 MeV is better than 0.4％. The total uncertainty for energy measurement of alpha particles emitted from the source is less than 5％.Environmental tests have also been performed. The results are satisfactory.