The differences of chemical composition in various layers of wheat straw were studied by infrared spectroscopy with OMNI sampler. The dependence of surface chemical composition of wheat straw on the processing methods was also studied. The results show that there is large amount of SiO2(-1,070 cm-1, -800 cm-1) in the surface of wheat straw. The out layer contains large amount of non-aromatic esters(nu c-o = 1,733 cm-1). There is few OH-containing (-3,300 cm-1) on the surface. The lignin(1,731, 1,650, 1,595, 1,505, 1,455, 1,425, 1,234, 1,039 and 835 cm-1) and cellulose(3,350, 2,935, 2,850, 1,650, 1,455, 1,430, 1,367, 1,317, 1,160, 1,034 and 891 cm-1) are the main species in the middle and inner layers of wheat straw. The large amount of surface SiO2 is mainly responsible for the poor adhesive property in the manufacture of the man-made board. Only a small amount of hydrocarbon and non-aromatic esters is dissolved out when treating the wheat straw with hot water, however, the aqueous NaOH treatment may make esters and SiO2 dissolved out, and then the processing of the man-made board becomes praticable.