Ag(Nb_(0.8)Ta_(0.2))O_3 ceramics were prepared by the traditional solid-state reaction method. The effect of CaF_2 addition on the structure and di-electric properties of Ag(Nb_(0.8)Ta_(0.2))O_3 ceramics was investigated. The addition of CaF_2 led the ceramics to a larger grain size and distortion of lattice. With the addition of 4.5 wt.% CaF_2, the permittivity of the ceramics increased from 442 to 1028, the dielectric loss decreased sharply from 6.12×10~(-3) to 8.6×10~(-4), and the temperature coefficient of capacitance decreased from 1834 ppm/℃ to -50 ppm/℃ (at 1 MHz). These results indicated that the high permittivity was related with a large grain size, a low grain boundary density, and the weak Ta-O or Nb-O bond strength caused by the addition of CaF_2.