Spectral emissivity can be considered as a surface thermal physical property of materials, which is widely applied in radiation thermometry, heat transfer calculation and so on. Tungsten is a significant metal, but its spectral emissivity is rarely reported. Based on energy contrast method, a device measuring spectral emissivity is built, which is composed of four parts: standard reference blackbody, a Fourier transform infrared (FTIR) spectrometer, sample heating chamber, and optical system. This device can measure the spectral emissivity of samples in the wavelength range of 3～20 μm, and the overall uncertainty of this apparatus is better than 5%. The normal spectral emissivity of pure tungsten is measured by this device at four temperatures (573, 673, 773, 873 K), and the effects of oxidation, temperature, wavelength and heating time on the normal spectral emissivity of pure tungsten are analyzed in detail. The results showed that the variations of the spectral emissivity of unoxidized pure tungsten at four different temperatures were basically similar, and the difference of these values was relatively small, however, the spectral emissivity rapidly increased when the sample was oxidized and the strong oscillations were found at some wavelengths. The effect of temperature on the spectral emissivity of pure tungsten was slight when the sample wasn’t oxidized, while the spectral emissivity rapidly increased with increasing temperature when the samples was oxidized. The spectral emissivity of pure tungsten decreased with increasing wavelength. When the surface of the sample was oxidized, four peaks appeared at 4, 9, 12.5 and 16.5 μm due to the interference effect between the oxide layer and the metal substrate. At 573 and 673 K, the spectral emissivity of pure tungsten does not change significantly with increasing heating time. However, as the temperature increased, the spectral emissivity increased with increasing heating time at 773 and 873 K. At 773 K, the rate of the spectral emissivity increasing with increasing heating is relatively fast, and the surface of pure tungsten begins to be oxidized with large oxidation rate. At 873 K, the increase of spectral emissivity with increasing heating time is relatively flat, and remains stable. In summary, the variation of spectral emissivity of pure tungsten is relatively stable at lower temperature and unoxidizedstate. As the temperature increases, the spectral emissivity increases rapidly and strong oscillation occurs at multiple wavelengths when the surface is oxidized. It can be seen that the spectral emissivity of pure tungsten is greatly affected by the heating time, temperature and wavelength. In practice, especially in radiation thermometry, if the spectral emissivity of pure tungsten is regarded as a constant, the measurement error will be large. This study will further enrich the data of spectral emissivity of pure tungsten, and provide reference for scientific research and applications.