Abstract: The high efficiency lapping of calcium fluoride crystal is the prerequisite of its ultra-precision polishing. Two kinds of abrasives, single crystal diamond and agglomerated diamond were chosen to prepare the fixed abrasive pad (FAP). A comparison of lapping performance between agglomerated diamond FAP and single crystal diamond FAP was made. And the role of different kinds of diamond abrasives in self-conditioning process of FAP was explored. The results show that the lapping efficiency of FAP embedded with agglomerated diamond abrasives is obviously higher than the FAP embedded with single crystal diamond. The material removal rate of FAP embedded with agglomerated diamond is more stable during the process, which means its self-conditioning performance is much better than the FAP embedded with single crystal diamond. When adopting the agglomerated diamond with a original size of 3 to 5 μm as the abrasives of FAP and a lapping load of 10 kPa, the material removal rate of calcium fluoride crystal can reach 13.0 μm/min and the average surface roughness R_a is 130.0 nm.