Microstructures-evolution of the boron carbide ceramic sample during sintering process was investigated by synchrotron radiation X-ray computed tomography (SR-CT) technique. The projection images of the sample were obtained during sintering process in real-time. Two-dimensional and three-dimensional reconstructed images were obtained by treating the projection images of different sintering periods with filter back projection arithmetic and digital image processing method. From the reconstructed images, three sintering stages of the boron carbide ceramic sample were clearly distinguished and several sintering phenomenon during the sintering process such as grain contact, sintering neck growth and pore spheroidization were observed. Densification rate of sintering process was analyzed from the porosity-sintering time and porosity-time Logarithm curves which were obtained from reconstructed images of boron carbide ceramic sample at different sintering time. Three sintering stages and linear relationship between porosity and time Logarithm in the middle stage of sintering which were described in the traditional sintering theories were clearly observed from the porosity-sintering time and porosity-time Logarithm curves. The experiment results are in concordance with the sintering theory and provide an effective experimental data for analysis the sintering process and the mechanical characteristics of ceramics in further .