Abstract: The structure and property of the high resolution α-γ coincidence spectrometer and its; applications in determining heavy nuclide qualitatively and quantitatively are described. At present, the energy resolution of the spectrometer is 0.25% (for 5.486MeV aaaaaaaaa particle,, FWHM is 13.8keV); the energy shift of peak is 0.05% during eight hours; nonlinearity is less than 0.2% for the energy region from 4 to 8 MeV.The α probe of the spectrometer mainly consists of a silicon-gold surface barrier detector with active area 50 mm2 or 314 mm2. The detector is cooled by thermoelectric technique with a low-power Peltier element. Its temperature is decreased form room tem-perature (25℃) to - 25℃. Thus its leakage-current is decresed by 2 orders of magnitude and the system noise is also decreased; the energy resolution of the spectrometer is thus-raised.A 40×35 mm well type Nal (T1) scintillation crystal with 20 mm in well diameter and 25mm in well depth is employed in the γ probe of the spectrometer. The well wall of crystal is covered with 0.5mm thick aluminium. The crystal active thickness is about. 10mm. Thus both the loss of low energy γ-rays and the background of high energy γ-rays are decreased. At the same time, the nuclide measurement sensitivity and accuracy of mixture source are raised by changing source position to be measured in the well.In this paper, the method is being applied to the determination of 241Am in the presence of large amount of Cm and fission products, for example, when the ratio of241Am/242Cm equals 2×10-5 (α activity). It is convenient and accurate to measure 238Pu and 241Am in which the ratio of a activity is in the region of 10-2-50. Besides, it can be applied to the absolute measurement of transplutonium nuclides. Its accuracy is better than±1%.