A theoretical model of the infrared spectral emissivity measurement of materials using the integrated blackbody principle was established. The effects of the effective emissivity of the non-isothermal integrated blackbody cavity, the observation coefficient and the temperature drop during the sample material push-out were investigated. The device of the infrared spectral emissivity measurement using the integrated blackbody principle was set up which used a Fourier-Transform infrared spectrometer as the infrared radiation detection instrument. The effective emissivity of the integrated blackbody cavity was simulated using Monte-Carlo ray tracing method and the associated validation experiments were carried out. The effects of non-ideal factors, including the size-of-source effect and linearity of the spectral responsivity, on the infrared spectral emissivity measurement using the integrated blackbody principle were investigated. The experimental measurements of the infrared spectral emissivity of a graphite material were carried out at 1000℃, 1300℃ and 1500℃, respectively. The results in this article are in good agreement with the literature data better than 5%, which verifies the feasibility of the emissivity measurement method using the integrated blackbody principle at high temperatures.