The Bi2Sr2CaCu2Ox(Bi-2212) multifilament round wires were fabricated by the powder-in-tube technique. Open ends and closed ends wires were heat-treated in 1atm flowing O2. Several samples at various points of the partial-melt processing were prepared. The influences of the gas content inside wires on the diameters, microstructures and the phase compositions were systematically investigated. The results showed that large amount of bubbles were residual during the partial melting process of Bi-2212 filaments in pure O2 atmosphere. Porosity agglonerated large bubbles on melting of the Bi-2212 powders. These bubbles were partially retained inside the final wires. High internal gas pressure would cause the molten phase towards the Ag layer to fill the defects, resulting the filament-to-filament bonding and the worse texture.