Abstract: To research fuel pebble dynamics in high-temperature gas-cooled reactor (HTR) further, a three-dimensional experimental platform of 10 MW HTR was built according to the scale of 1∶5 by the Institute of Nuclear and New Energy Technology, Tsinghua University. The multi-slice helical CT was used to detect pebble motion in simulated reactor core. Simulated pebbles were normal balls and target balls with identical appearances and masses. The procedure of CT detection of pebble trajectory was simulated in this paper. The reconstructed images of target balls in different time, different locations were simulated. Then the reconstructed images were analyzed, target balls were identified and their transverse (x, y) and perpendicular (z) coordinates were located. As to the situation of multi-target ball, the matching criterion was determined. The target balls were matched and marked with different colors (c). The five-dimensional (x, y, z, t, c) history trajectory information of target balls was wholly reshaped and displayed by animation. This paper provides an important reference to the research of pebble dynamics in HTR.