Polycrystalline half-metallic Fe3O4 films fabricated by facing-target reactive sputtering were investigated systemically. Structural results reveal that typical Fe3O4 grains were well isolated by grain boundaries and grew with columnar structure. The room-temperature magnetization of Fe3O4 films at 50 kOe field is much lower than that of bulk Fe3O4(471 emu/cm3), due to the presence of strong antiferromagnetic coupling within grain boundary and the amorphous bottom and top layers. The insaturation magnetization and loop shift in high field region at low temperature also stem from the strong antiferromagnetic coupling. The resistivity increases with the decreasing temperature and is consistent with fluctuation-induced tunneling mechanism in a wide temperature ranging from 50 to 300 K. The negative magnetoresistances up to -9.7% at 150 K and -6.4% at 300 K under 90 kOe magnetic field perpendicular to the film plane were observed and discussed.