Linker length is one crucial factor affecting the free radical scavenging activity of curcumin. However, identifying an optimal linker length that maintains the desired activity remains challenging. This study offers a thermodynamic evaluation of the influence of linker length on free radical scavenging activity of curcumin, specifically through the hydrogen atom transfer mechanism, in water solvents. Our first-principles calculations reveal that both elongating and shortening the linker promotes a more favorable hydrogen atom transfer at the phenolic O─H and the C─H bond within the linker, respectively. Therefore, linker length should be considered in developing curcumin as a multifunctional medicine.