Abstract: In order to investigate the influences of foaming agent azodicarbonamide (AC) additive amount on the thermo-stability, microstructure and chemical structure of wheat straw/polypropylene (PP) foamed composites, TG-DSC, FTIR and stereomicroscope were used to analyze the thermo-stability, chemical structure and microstructure of wheat straw/PP foamed composites, and linear expansion coefficient, thermal conductivity, apparent density and mechanical properties of composites were also measured. The results show that AC additive amount and its thermal decomposition degree both have great influences on the thermo-stability, pore structure and thermal expansion properties of wheat straw/PP foamed composites. When AC additive amount is 1.0wt%, the thermal decomposition degree is the highest, and the composites have relatively preferable thermo-stability, the pore structure is homogeneous, interface between wheat straw and matrix is stable, and the linear expansion coefficient is the lowest. The conclusions obtained indicate that when AC additive amount is 1.0wt%, the wheat straw/PP foamed composites have relatively preferable comprehensive performance.