Abstract: The outlet of wastewater containing arsenic is one of the greatest potential safety hazards in the source of drinking water. Spent grains modified by inorganic salt used as adsorbent to treat water with low concentration arsenic is studied in this paper. The optimal modification condition is the well mixture of 1.5 mol/L NaCl with grains at ratio of 1 L∶100 g and modification for 12 h at room temperature. Without adjusting the pH value (the solution pH was 7), when modified grains dosage is 5 g/L, the initial arsenic concentration 0.1 mg/L can reach the adsorption equilibrium at 60 min. The arsenic in effluent can meet the requirement of the arsenic content of 0.01 mg/L in “Standards for Drinking Water Quality” (GB5749-2006). The influence of coexisting anions on the arsenic adsorption by NaCl modified spent grains is investigated, and the effect of the NaCl modified spent grains used for treating actual arsenic-containing source water is testified.