Salt stress represents a significant abiotic stressor for plants and poses a severe threat to agricultural productivity. Glutaredoxins (GRXs) are small disulfide reductases that can scavenge cellular reactive oxygen species and are crucial for plant growth and development, particularly under stressful circumstances. Although CGFS-type GRXs were found to be involved in various abiotic stresses, the intrinsic mechanism mediated by LeGRXS14, a tomato (Lycopersicon esculentumMill.) CGFS-type GRX, is not yet fully understood. We discovered that LeGRXS14 is relatively conserved at the N-terminus and exhibits an increase in expression level under salt and osmotic stress conditions in tomatoes. The expression levels ofLeGRXS14in response to osmotic stress peaked relatively rapidly at 30 min, while the response to salt stress only peaked at 6 h. We constructedLeGRXS14overexpressionArabidopsis thaliana(OE) lines and confirmed that LeGRXS14 is located on the plasma membrane, nucleus, and chloroplasts. In comparison to the wild-type Col-0 (WT), the OE lines displayed greater sensitivity to salt stress, resulting in a profound inhibition of root growth under the same conditions. Analysis of the mRNA levels of the WT and OE lines revealed that salt stress-related factors, such asZAT12,SOS3, andNHX6,were downregulated. Based on our research, it can be concluded thatLeGRXS14plays a significant role in plant tolerance to salt. However, our findings also suggest thatLeGRXS14may act as a negative regulator in this process by exacerbating Na+toxicity and the resulting oxidative stress.