The synergistic influence of carbonized straw fiber and diatomite on the formaldehyde purification performance of straw cement-based composite was studied.The results shown that the micro pores and specific surface area of low-grade diatomite calcined at 600℃ were increased.After 20 minutes of carbonization in vacuum at 200℃,the capillary of straw fiber became more transparent,and the specific surface area of straw fiber before and after carbonization increased nearly 34 times.When the content of diatomite accounts for 25% of the cementitious material,the purification rate of the original straw cement-based composite for formaldehyde in 24 hours was 82.65%,and the lasting purification rate was 51.96%.After lasting purification rate was 55.37%.The synergistic influence of carbonized straw fiber and diatomite significantly improved the formaldehyde purification ability of the composite.