The invention relates to a core clamping mechanism. The core clamping mechanism is provided with a cylindrical clamp holder barrel, wherein the inner hole of the barrel is conical and is coincided with the outer wall of an oppositely-opened conical sleeve; one end of the barrel is provided with an external thread which is connected with a burden pressure cylinder, and the other end of the barrel is provided with an internal thread which is connected with an end sleeve; the inner hole of the oppositely-opened conical sleeve is cylindrical; a thin-wall Hastalloy barrel is arranged in the oppositely-opened conical sleeve; the outer wall of the thin-wall Hastalloy barrel is cylindrical and is coincided with the inner hole of the oppositely-opened conical sleeve; the large-head section of the oppositely-opened conical sleeve is provided with external threads and is fastened by a fastening nut; an experiment core is arranged in the thin-wall Hastalloy barrel; an end surface on the upstream of the core is contacted with a burden pressure plug; the burden pressure plug is extended out of the burden pressure cylinder; an end surface on the downstream of the core is contacted with a downstream plug; and the downstream plug is extended out of the end sleeve. By the mechanism, the accuracy of an experiment result is ensured.