Sandy soil is a common geotechnical material. To satisfy the mechanical and environmental requirements in engineering, the granulated blast furnace powder (GGBS) as a solid waste discharged by steel industry can replace cement as a soil curing agent. In this study, GGBS was used as curing agent and magnesium oxide (MgO) was used as stimulating agent to reinforce the sand. The influence of curing age (3, 7, 14, 28, 56 days) and the mixing amount of curing agent (8%, 10%, 12%) and the amount of magnesium oxide (0%, 5%, 10%, 15%, 20%, 40%) on the strength development rule of curing soil were analyzed. The results showed that under the same amount of curing agent, the unconfined compressive strength of cemented sand has no obvious relation with curing age less than 7 days. However, when the curing age was longer than 7 days, the longer the age period was, the higher the unconfined compressive strength of the sand soil was. Furthermore, the amount of curing agent is positively correlated with the unlimited compressive strength of sand. Finally, although magnesium oxide dosage can promote the improvement of the unlimited compressive strength, excessive magnesium oxide would inhibit the increase of the unlimited compressive strength in sand. The strength characteristics of GGBS-MgO treated sand were studied in laboratory experiments, which can provide a theoretical basis for field engineering application.