It was reported that TiB2 gains grew fast during sintering was a main cause for its properties degrading.In this paper the HP-sintering mechanics of TiB2 was studied and the results show that grains grow very fast when the sintering temperature is near 1800℃. From the sintering dynamics, it can be concluded that grain fast growing results in boundary-transporting processing, during which grain boundary work as fast tunnel for material transporting.