Bi_2.1Sr_1.96CaCu_2.0O_8+d (Bi-2212) precursor powders were synthesized with co-precipitation process, and Bi-2212 single filament tapes were fabricated with powder-in-tube (PIT) technique. Based on SEM observation, the primary grain size of Bi-2212 precursor powders was 3~5 mm. However, after sintering, Bi-2212 grains clustered together and the particle size distribution became quite wide, from 10 mm to over 180 mm. By dividing the particles into four groups with different average particle size, the influences of average particle size on the filament density, microstructures and current capacity of final Bi-2212 tapes were systematically investigated. It was observed that with the decrease of particle size, the filament density increased over the entire cold-working process and heat treatment process. Therefore, the intergrain connection was enhanced, which lead to the obvious increase of current capacity