The performance and wear mechanisms of two types of polycrystalline diamond (PCD) cutting tools (marked as PCD 010 and PCD 030) have been investigated in this paper. Continuous turning of round granite bars has been selected as the test method. The Taylor equation has been developed to describe the tool performance. The experimental results indicate that PCD 010 has a greater thermal wear resistance than PCD 030 at high cutting speeds. Scanning electron microscopy (SEM) was used to evaluate wear mechanisms of PCD tools, our results show that the dominant wear mechanisms for PCD 010 is abrasion wear while that for PCD 030 is inter-granular and cleavage wear.