Abstract: Sites and soils treated with solidification/stabilization remediation have received much attention due to the residual pollutants in the soil. The solidified/stabilized heavy metals may be reactivated under environmental stress, and the rate and form of reactivation are unknown. It is hot and rainy in South China, with frequent and intense heat and humidity exchanges. Therefore, the use of solidified/stabilized sites are at greater risk. Typical solidified/stabilized soil samples were collected from two sites in the Pearl River Delta region to study the effect of flooding and dry-wet alternation on the release and transformation of chromium (Cr) in soil. The results showed that: (1) Flooding and dry-wet alternation increased the Cr leaching concentration. Compared with pre-flooding, the Cr leaching concentration of soil from Sites A and B increased by 1.32 and 8.72 times, respectively. After dry-wet alternation, the Cr leaching concentration of soil from Site A decreased slightly, while the Cr leaching concentration from Site B increased by 4.32 times. (2) Flooding and dry-wet alternation promoted the Cr conversion from the acid extractable state to the relatively stable oxidizable state. Compared with pre-flooding, the acid extractable Cr content of soils from Sites A and B decreased by 60.17% and 14.34%, respectively, and the oxidizable Cr content increased by 2.71% and 13.30%, respectively. After dry-wet alternation, acid extractable Cr content of soils from Sites A and B decreased by 28.78% and 2.13%, respectively, while the oxidizable Cr content increased by 5.48% and 10.22%, respectively. (3) Flooding affected Cr stability by reducing soil oxidation-reduction potential (E_h), pH, and amorphous iron oxides, promoting the Mn⁴⁺ reduction, Fe³⁺ reduction, and Cr re-release. Dry-wet alternation had less influence on the solidified/stabilized system than flooding. This study also showed that water stress increased the Cr leaching concentration of solidified/stabilized soils and changed the Cr occurrence forms, but the leaching concentration was much lower than the Toxic Leaching-Related Limit Specified in the Identification Standards for Hazardous Wastes: Identification for Extraction Toxicity (GB 5085.3—2007) and Environmental Protection Technical Specifications for Pollution Treatment of the Chromium Residue (on trial) (HJ/T 301—2007). In consideration of the long-term and complex environmental stress and the inadequate subsequent supervision of solidified/stabilized sites caused by the current ‘determined by one assessment’ effect evaluation management mode, continuous attention and systematic management are necessary for sustainable and safe utilization of the solidified/stabilized sites.