This paper discusses blending properties of gypsum fiberboard (GFB) by semi dry process. 4 kinds of blending were examined by means of surveying the granule size of admixture, testing moisture content ( MC ), scanning electron microscopy (SEM), etc. The results showed that for semi dry process, 3 kinds of blending methods were available in which the side effects of airflow blending method was lowest. The granule size of admixture played a central part in the bending strength of GFB, the bigger the granule size of admixture, the lower MOR of GFB. The admixture homogeneity depended upon both ratio of water/gypsum ( H/G ) and ratio of wood/gypsum ( W/G ) which could be described by k function.