With the aim of treating soluble salt diseases in sand and stone cultural relics, we propose a method of using sodium octaborate to inhibit sodium sulfate crystallization. The inhibitory effects of gradient concentrations of sodium octaborate on sodium sulfate crystallization of sandstone from northern Shaanxi were studied using polarized light microscopy, scanning electron microscopy and X-ray diffraction. The results show that the greater the concentration of sodium octaborate was, the less sodium sulfate crystallized out. Taking into account the principle of “minimal intervention in cultural relic conservation”, a sodium octaborate solution with a mass fraction of 15% was selected as the best salt-inhibiting concentration. This research has important theoretical and practical significance for the treatment of soluble salt diseases and the conservation of sand and stone cultural relics.