Abstract: This paper is aimed at the problem of reducing carbon emissions of cement and its composites under the carbon peaking and carbon neutrality goals. This study used corn straw waste (CSW) as raw material to develop a three-step process of pretreatment-pyrolysis-grinding to prepare a sustainable corn straw ash (CSA) material that can be used as supplementary cementing materials. The study focused on studying the effects of pretreatment methods (untreated, distilled water washing, hydrochloric acid washing), pyrolysis temperature (500℃, 600℃, 700℃) and pyrolysis durations (1 h, 2 h, 3 h) on CSA activity, as well as the effects of different pretreatment types and blending amounts of CSA on the performance of prepared mortars. The experimental results show that the content of SiO₂ of CSA increases with the enhancement of pyrolysis temperature and duration. And the effect of pyrolysis temperature on SiO₂ crystallization is much greater than that of pyrolysis durations. The incorporation of 5wt% CSA increases the compressive strength of mortar by 11.7%. The incorporation of over 5wt% CSA decreases the compressive strength due to the porous structure of CSA. The incorporation of untreated, distilled water washing and hydrochloric acid washing CSA demonstrated causes the hydrate calcium silicate (C-S-H) morphology in the cement matrix to change from honeycomb and fibrous to dense gel. The CSA treated by acid washing and pyrolysis at 600℃ for 2 h shows excellent pozzolanic activity and can be used as good supplementary cementing materials.