The cost of the new bit accounts for 40% of the total of penetration operation. So that it becomes urgnt to prolong the service life of bit and cut down peneteration cost. Under given conditions, the service life depends mainly on performance and properties of the bit. In order to have a correct measurement of its performances, a theoretical basis and scientific methods are required to determine the measurement. Therefore, the author proposes two concepts, i.c. sharpness and wear-resistance, to evaluate the performances of diamond-set bit thus offering converience for quantified performance testing.