The BiFeO3 nano-powder has been synthesized by sol-gel method. The structure and morphology of BiFeO3 nano-powder have been characterized by X-ray diffraction （XRD），scanning electron microscopy （SEM） and high resolution transmission electron microscopy （HRTEM）. The results showed that the samples sintered at 700℃ for 2 h or 25 h is in the formed of pure BiFeO3 with the grain size about 30 nm，and the structure is hexagonal of R3-m［166］ space group with lattice constants a=b=05580 nm，c=06939 nm，and the spacing of （101） and （110） are about 0396 nm and 0273 nm，respectively. The room temperature magnetic properties of samples have been measured on vibrating sample magnetometer （VSM）. It was showed that the BiFeO3 nano-powder gives a complete hysteresis loop，which means that BiFeO3 nano-powder possesses weakly ferromagnetic at room temperature，its coercive force （Hc） could reach to over 700 Oe，and the magnetic mechanism comes from the double exchange of Fe3+-O-Fe2+. Moreover，with the increase of the sintering time，the grain size is influenced；the saturation magnetization （Ms） has a small change，however，the coercive force （Hc） of the BiFeO3 nano-powder decreased obviously.