The spatiotemporal substitution method was used to collect yellow soil and purple soil with different acidification degrees； analyze the effects of acidification on the composition and properties of soil aggregates； explore the distribution characteristics, occurrence forms, and availability of arsenic （As） in soil aggregates with different acidification degrees； and reveal the key factors restricting the availability of soil As. The results showed that the distribution of total As in each aggregate was positively affected by its mass fraction, and the larger the mass fraction, the more the total As distribution. Soil acidification destroyed the aggregate structure, reduced the mass fraction of large aggregate S1 （>
2 mm） by 5 to 15 percentage points, led to the increase in amorphous iron content by 2 to 7 times, and decreased the total As distribution of S1. The available As was positively regulated by non-obligate/obligate adsorptive arsenic （F1, F2） （F1+F2 correlation coefficient 0.76） and negatively affected by residual arsenic （F5） （correlation coefficient -0.89）. Soil acidification significantly reduced the ratio of F1 to F2 after exogenous As entered the soil, resulting in a decrease in