Using the X-ray diffraction techniques, the intensity, structure factor, pair distribution function and the nearest neighbor distance of non-crystalline alloy Mg70Zn30 were obtained. The experimental results show that there is a visible pre-peak on the structure factor of non-crystalline alloy Mg70Zn30 in the small Q region. According to the characters of the pre-peak, an atomic model of Mg70Zn30 melt was constructed, namely, a bcc structure with one Mg atom locates at the center and other eight Zn atoms lie on the vertexes. Combined with shared vertex, it can meet the requirement for the distance of Mg-Mg atoms. The origin of the pre-peak on the structure factor of non-crystalline alloy Mg70Zn30 is caused by the correlation between the central Mg atoms in neighboring clusters.